This document discusses water pollution and eutrophication. It defines different types of water pollutants and methods for monitoring pollution, including direct chemical measurements and indirect biological indicators like BOD and indicator species. Eutrophication occurs when a water body receives too many nutrients, causing algal blooms that reduce oxygen levels. Symptoms include decreased biodiversity and dissolved oxygen. Management strategies include reducing nutrient inputs from fertilizers and sewage, removing pollutants from water, and regulations on industries and public behaviors.

1. Topic 4
Water and aquatic food production
systems and societies
4.4 Water pollution

2. Types of Water Pollutants
• Floating debris
• Organic (decaying) matter (e.g. sewage)
• Inorganic nutrients (phosphates and nitrates)
• Heavy metals
• Synthetic materials (e.g. discarded plastics)
• Suspended solids
• Heat
• Oil spills
• Radioactivity
• Invasive (alien) species

3. Monitoring Water Pollution
• Nitrate concentration
• Nitrite concentration
• Free chlorine
• Chloride concentration
• Hardness (mineral content)
• Heavy metals
• Turbidity (suspended solids)
• BOD
• COD
• Biological indicators
Direct
measuremen
t (chemical
indicators)
Indirect
measuremen

4. Biochemical Oxygen Demand (BOD)
• The more respiring microorganisms in a sample of
water, the faster the oxygen in it will be consumed –
i.e. the higher its BOD
• You could also take a sample of water and seed it with
a known concentration of a known species of bacteria.
A measurement of how quickly the dissolved oxygen in
the water is consumed (in the dark) will then give an
indirect measurement the quantity of organic matter
(substrate) in the sample.
• Generally 3 day or 5 day BOD measurements are made
at 20oC in order to standardise the test (BOD3; BOD5)

5. Indicator Species
• Certain species (usually invertebrates) are indicative of
water bodies of specific quality
• High biodiversity of such species is indicative of the
absence of organic pollutants
• Low biodiversity and a change to only specific tolerant
species is indicative of pollution
• There is usually a direct link between the BOD
concentration in a water body and the biodiversity of
indicator species
• It is a quick and direct method of estimating levels of
pollution

6. The Trent Biotic Index
• Turns your measurements of the biodiversity of indicator species
into a scale (1 – 10), using a chart:

7. What is Eutrophication?
Water body receives too much nitrogen and/or phosphorus
Algal blooms occur due to increased nutrient availability
Increased levels of phytoplankton and algae cut off light to submerged plants
Decomposition of plant material and build up of bacterial populations
Oxygen levels in the water body fall significantly and it
becomes anoxic and unable to support life

8. The Symptoms of Eutrophication
• Increased turbidity
• Increased sedimentation,
reducing water flow, filling in
lakes
• Decreased dissolved oxygen
concentration
• Decreased biodiversity of primary
producers. Loss of submerged
macrophytes
• Toxic cyanobacterial blooms
• Decreased biodiversity of
consumers: fish population
dominated by surface-dwellers
such as pike and perch
http://www.youtube.com/watch?v=0JnKkit5ocI

9. The Impacts of Eutrophication
• Economic losses to farmers due to loss of
fertiliser from soil
• Health effects from drinking nitrate-rich water
(some disputed links to increased rates of
stomach cancer and blue baby syndrome)
• Loss of water bodies as a public amenity and
scarring of the landscape
• Loss of biodiversity

10. Management Strategies
1. Reduction (Altering human activities):
– Avoid over-use of artificial fertilisers
– Match fertiliser use carefully to the crop
– Reduce use of fertilisers between mid-September and mid-
February when leaching rates are highest (in the Northern
Hemisphere)
– Give preference to leguminous plants – their roots fix
nitrogen and reduce dependence on fertiliser
– Match fertiliser use carefully to the crop
– Do not apply fertiliser or keep animals close to water
bodies
– Do not plough-up grassland (this released nitrogen)
– Use flat terrain for crops to reduce loss through leaching

11. Management Strategies
2. Removal (Clean-up):
– Removal of nutrients by precipitation (e.g. aluminium
or iron salts can be added in order to produce
phosphate precipitates which can be easily removed
and disposed of)
– Removal of nutrient-rich sediments (e.g. by dredging)
– Removal of biomass from affected water bodies (e.g.
removal of predatory fish to allow primary consumers
to recover)
– Prevention of point-source pollution which is known
to be responsible for eutrophication (e.g. nutrient
stripping of effluents, or improved treatment of
sewage effluents to remove nutrients)

12. Management Strategies
3. Regulation (and public campaigns):
– Introduction of phosphate-stripping at sewage
works (by biological nutrient removal or
precipitation)
– Switching to phosphate-free detergents
– Using washing machines only for full-loads
– Reduced use of fertilisers on lawns and public
places
– Punishments for not collecting animal poo
– Compost organic waste rather than send it to
landfill