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14.6 Fertilisers and the environment

14.6 Fertilisers and the environment (ESCSS)

This section can be taught using the suggested class discussion.

The fertiliser industry is a very important industry in South Africa and in the world. It helps provide the nutrients that we need to ensure healthy crops to sustain life on Earth. However, fertilisers can also harm the environment if they are not used in a responsible manner. This section will focus on some of the environmental problems that excessive use of fertilisers can cause.

Eutrophication (ESCST)

Eutrophication (Figure 14.12) is the enrichment of an ecosystem with large quantities of chemical compounds, mostly containing the nutrients nitrogen and phosphorus. Eutrophication is considered a form of pollution because it promotes excessive plant growth, favouring certain species over others. In aquatic environments, the rapid growth of certain types of plants can disrupt the normal functioning of an ecosystem, causing a variety of problems. Human society is impacted as well, as health-related problems can occur if eutrophic conditions interfere with the treatment of drinking water. Eutrophication can also decrease the resource value of rivers, lakes, and estuaries.

Figure 14.12: An example of the effect of eutrophication (algal bloom).

Eutrophication refers to an over-supply in chemical nutrients in an ecosystem, leading to the depletion of oxygen in a water system through excessive plant growth. These chemical nutrients usually contain nitrogen or phosphorus.

In some cases, eutrophication can be a natural process that occurs very slowly over time. However, it can also be accelerated by certain human activities. Agricultural runoff, where excess fertilisers are washed off fields and into ground water, and sewage, are two of the major causes of eutrophication. The impacts of eutrophication are the following:

  • A decrease in biodiversity (the number of plant and animal species in an ecosystem)

    When a system is enriched with nitrogen, plant growth is accelerated. When the number of plants increases in an aquatic system, it can block light from reaching deeper water. Plants also consume oxygen for respiration, depleting the oxygen content of the water, which can cause other organisms, such as fish, to die.

  • Toxicity

    In certain instances the plants that flourish during eutrophication can be toxic and these toxins may accumulate in the food chain.

A buffer zone is an area that lies between two other areas, for example, a farm and a river. It is an area of land designated for environmental protection.

Despite these impacts, there are a number of ways to prevent eutrophication from taking place.

Prevention of eutrophication:

  • Clean-up measures can directly remove the excess nutrients such as nitrogen and phosphorus from the water.

  • Creating buffer zones near farms, roads and rivers can also help. These act as filters and cause nutrients and sediments to be deposited there instead of in the aquatic system.

  • Laws relating to the treatment and discharge of sewage can also help to control eutrophication.

  • A final possible intervention is nitrogen testing and modelling. By assessing exactly how much fertiliser is needed by crops and other plants, farmers can make sure that they apply only the required amount of fertiliser. This means that there is no excess to run off into neighbouring streams when it rains. This includes a cost benefit for the farmer as they are less likely to waste fertiliser.

South Africa's Department of Water Affairs and Forestry has a National Eutrophication Monitoring Programme, which was set up to monitor eutrophication in impoundments such as dams, where no monitoring was taking place.

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Dealing with the consequences of eutrophication

In many cases, the damage from eutrophication is already done. As a class, discuss the following:

  1. List all the possible consequences of eutrophication that you can think of.

  2. Suggest ways to solve the problems that arise because of eutrophication.

  3. Discuss how the public can help to prevent eutrophication.

  • This investigation should be handed out before this section is taught so that learners can have their results by the time this section is started.

  • The last teaching lesson can be spent working on the interpretation and recommendations of their findings.

  • Teachers can decide in what format they want the investigation handed in – a written report, poster, or oral presentation.

Fertiliser in your area

For this investigation you will be working in a group. Your task is to find out what fertilisers are used in your area and whether people know about the impact of fertilisers on the environment, especially the water sources in the area.

  1. Design a survey to find out the following:

    • Do people use fertilisers in their gardens or the areas around their homes?

    • What type of fertilisers are they using?

    • Why are they using fertilisers?

    • How often do they apply fertilisers?

    • How much fertiliser do they use in each application?

    • Do they use organic or inorganic fertilisers?

    • Which ones do they think are better to use?

    • How do they think fertilisers influence the quality of water in the area?

  2. Collect your data

    Take the survey to at least \(\text{10}\) people in your area. Record their responses.

  3. Present your findings

    Present your findings in tables or graphs and write a one-page summary of what you have found.

  4. Interpret your findings

    Discuss your findings:

    • Answer all the questions that were posed in the beginning of the investigation.

    • Did you find what you thought you would?

    • What was different?

    • What was the same?

    • Why do you think this is the case?

  5. Make recommendations

    Include some recommendations to people in your neighbourhood regarding the use of fertilisers and their impact on the environment.

    Suggestion: Report your findings in your local newspaper to promote awareness.