Human influence on the nitrogen cycle

• Farming : plants absorb nitrates from soil. Plants are harvested and nitrogen is not returned to soil by decomposition.
• We eat plants, nitrogen does not go back to soil but in sewage. Little nitrogen is left in soil, fertilizers are then used.
• Wetlands use too many nitrates. Because fertilizers wash into rivers. Extra nitrates cause algae to grow, algae die and decay, decomposers in water use up a lot of oxygen, organisms in water die
• Eutrophication: Excess algae growth owing to an abundant supply of plant nutrients, which causes problems for other organisms in the system