pollution and nutrient cycles

• Eutrophication of sewage, manure, fertilizers

  1. washed of fields by rain into lakes, rivers, streams
  2. contains phosphates and nitrates
  3. algae blooms on the surface
  4. blocks the sunlight from other under water plants so they cannot photosynthesis and die
  5. the population of decomposers and bacteria breakdown the plants using oxygen (respiration)
  6. less oxygen in water so fish and aquatic life suffocate and die
• Indicator species

  1. air pollution

  • lichens are commonly used to determine air pollution as they will only grow in areas which are free from air pollutants produced by traffic

  1. water pollution

  • determined by the fall in oxygen levels or change in pH
  • can often judge the level of pollution by plants and animals, some may be absent because of pollution whilst others may only be there because of the pollution, invertebrates
• Bioaccumulation: chemicals do not break down so they build up in the food chain over time (DDT, mercury, pesticides)

  1. pollutant washed into rivers and lakes
  2. enters food chain being absorbed by producers
  3. producer is eaten, the pollutant is passed onto the next trophic level, remains in organism
  4. pollutant continues to accumulate, increasing in concentration, as it moves up the food chain.
  5. reaches the top carnivore, the pollutant has accumulated to such an extent that it becomes toxic, causing reduced fertility or even death.
• DDT is a chemical used by famers to kill insects eating crops

  • it has been shown to cause weakened shells in birds of prey eggs
  • they then don't survive which causes the population to decrease

  
• The carbon cycle

  Carbon is passed from the atmosphere, as carbon dioxide, to living things. It is then passed from one organism to the next in complex molecules, and returned to the atmosphere as carbon dioxide again. This is known as the carbon cycle

  
• removing carbon from atmosphere:

  photosynthesis - carbon atoms become incorporated into organic substances

  • passing carbon onto the next organism animals get their carbon through eating plants or other animals
• adding carbon to atmosphere:

  • respiration
  • combustion
  • decomposition - happens faster in warm, moist conditions with plenty of oxygen because it involves micro-organisms. Decay can be very slow in cold, dry conditions, and when there is a shortage of oxygen.
  • volcanic activity
• carbon from human activities:

  • humans only been extracting and burning fossil fuels the last 200 years
  • this has disrupted the balance and led to an increase in levels of carbon dioxide in the atmosphere
  • burning fossil fuels releases the carbon atoms in the undecomposed plants that formed them
• The nitrogen cycle

  Nitrogen compounds found in cells include proteins. Nitrogen from the air is converted into soluble ions that plant roots can absorb. It forms part of nitrogen compounds in the plants, and is then passed from one organism to the next. It is returned to the atmosphere as nitrogen gas. This is the nitrogen cycle.

  
• Nitrogen fixation


  1. Nitrogen gas converted to nitrogen containing compounds in soil which plants use

  2. Lightning making nitrogen react with oxygen in air

  3. Nitrogen fixing bacteria in roots of legumes (beans, peas, clover) turning nitrogen gas to nitrogen compounds that plants use to make proteins
• Plants absorb


  Nitrates into the roots
• Nitrogen cycle


  1. Moving along the food chain and excretion

  2. Excretion of urea releases nitrogenous compounds into soil

  3. Bacteria in soil make an enzyme called urease which converts this urea into ammonia

  4. Nitrifying bacteria convert ammonia into nitrates which plants can absorb

  5. Death of animals, Decomposers break down protein in dead bodies of animals and plants, converting it into ammonia

  6. Nitrifying bacteria then convert ammonia into nitrite, and then nitrates

  7. Denitrifying bacteria in soil break down nitrates and return nitrogen gas to air, occurs in anaerobic conditions
• Denitrification


  1. Denitrifying bacteria break down nitrates

  2. Return nitrogen gas to the air

  3. Occurs in anaerobic conditions
• Farmers try to prevent denitrification as plants grow best when there are plenty of nitrates in the soil for them to use to make the proteins they need for growth
• Preventing denitrification


  1. Plough the soil regularly to encourage aerobic conditions (get oxygen in)

  2. Drain any waterlogged areas
• Increasing soil fertility


  1. Rotate crops by planting leguminous plants every few years

  2. These have root nodules filled with nitrogen-fixing bacteria

  3. Nitrogen-fixing bacteria can convert nitrogen gas directly from the air into nitrogenous compounds the plants can use
• Adding fertilisers