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FRESHWATER POLLUTION
The Effects of Pollution Caused by
Treated Domestic Sewage on a
Freshwater Ecosystem
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
Solid storage
Sewage is stirred
by a propeller. separation. Farmers collect
Liquid >it in Autumn
This increases its
continues onto >and Winter to
surface area.
biological >be used as
Air (esp. treatment. >organic
Oxygen) mixed >fertiliser.
with the sewage.
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Biological Treatment:
Urea from domestic sewage 2NO2- + O2 2NO3-
breaks down into Ammonium (Carried out by nitrobacter)
(NH4+). Nitrobacter use the Nitrites
Aerobic bacteria carry out from the previous reaction
oxidation reactions, and produce Nitrates (NO3-).
converting the ammonium Both reactions use up
ions to nitrate. Oxygen.
The reactions: Nitrosomonas and
nitrobacter occur naturally in
2NH4+ + 3O2 2NO2-+ 4H+ watercourses therefore if the
(Carried out by nitrosomonas) treatment process is
Ammonium is used as food insufficient, the ammonia will
be converted to nitrate and
for Nitrosomonas to produce cause Oxygen depletion in
nitrite (NO2-). the receiving water.
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Abiotic Hypothesis:
Abiotic Variable Site 1 Site 2
(Control) (Outfall)
Oxygen %
pH
Temperature
Nitrate
Phosphate
Ammonium
Dissolved Load 7
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 how To determine the
treated sewage affects susceptibility of
the abiotic conditions: freshwater
Oxygen concentration invertebrates to organic
pollution, using
Temperature indicator species to give
pH an indication of the
Ammonium extent of long term
Nitrates pollution.
Phosphates To determine the
effects of pollution on
Dissolved Load species diversity and
abundance.
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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
12
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
13
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
16
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
20
This shows
freshwater
fauna as
indicators
of river
pollution.
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