Fertilisers and eutrophication

Describe the steps of Eutophication

1. Leaching of phosphates/ nitrates into lakes

2. Algal bloom which blocks sunlight

3. Surrounding plants die as they can’t photosynthesise

4. Saprobionts decompose dead plant matter, using O₂ in aerobic respiration

5. Less O₂ for fish to aerobically respire so they die

Explain why fertilisers are used?

• To replace nitrates/ phosphates lost when plants are harvested and livestock are removed 

• Those removed from soil and incorporated into biomass can’t be released back into the soil through decomposition by saprobionts

• So improve efficiency of energy transfer - increase yield

Describe the difference between artificial and natural fertilisers

• Natural: organic, eg. manure, compost, sewage → ions released during decomposition by saprobionts

• Artificial: contains inorganic compounds of N, P and K

Explain the key advantage of using natural fertiliser over artificial fertiliser

• Less water soluble so less leaching → eutrophication less likely

• Organic molecules require breaking down by saprobionts → slow release of nitrate/ phosphate