Agriculture & Water Quality (DP IB Geography)

Revision Note

Agricultural Pollution & Water Quality

  • Agriculture can impact on water quality in a number of ways

    • Wastewater from silage and slurry

    • Fertilizers, herbicides and pesticides

    • Soil erosion

  • One of the main impacts of agriculture is eutrophication

Eutrophication 

  • Eutrophication is caused by an increase in the amount of nitrogen and phosphorus that is carried into streams and rivers from slurry and fertilizers

  • This leads to nutrient enrichment

Diagram depicting the process of nutrient pollution causing algal blooms and oxygen depletion in water. Six labeled steps illustrate the impact.
The process of eutrophication
  • Algae blooms increase because of higher nutrient levels caused by eutrophication, which causes a positive feedback loop

    • Increased algae blooms lead to increased decomposition as light cannot reach aquatic plants

    • Which decreases oxygen levels 

    • This reduces consumers and further increases algae growth

  • Anoxia can occur in the autumn season

  • Dead zones occur near boundary points between river mouths and coastal zones

  • There are three main reasons why eutrophication is a problem:

    • Nitrogen can cause excessive growth of algae

    • It can affect human health

    • A loss of fertiliser is an economic loss for agricultural production

  • There are several ways of resolving eutrophication:

    • Use different types of fertilisers and detergents, which may alter human effects of pollution

    • Pump mud from eutrophic water

    • Remove nitrates and phosphates from water

  • Reducing nitrate loss in the Northern Hemisphere:

    • Barley straw uses nitrogen in the process of decay

    • When soils are wet, avoid using nitrogen fertilisers

    • Avoid applying nitrogen fertilisers to fields next to streams or lakes

    • Avoid ploughing grass as it releases nitrogen

    • Avoid applying fertiliser if rain is forecast

      • Use barley straw to prevent the growth of algae

Irrigation & Water Quality

Irrigation

  • Irrigation has been taking place since ancient times

  • Water for irrigation can be taken from surface stores

  • There are various types of irrigation including:

    • Total flooding, such as in rice fields

    • Sprinklers

    • Drip systems

Salinisation

  • Salinisation may occur due to an increase of salt in the soil left as the water evaporates

  • Groundwater levels can be close to the surface

  • Capillary forces can bring water to the surface and then evaporation occurs

  • When evaporation occurs, soluble salts will be left behind

  • These salts make the land toxic to many crops, so the land can no longer be used

    • Salinization in San Joaquin Valley, California, was projected to cost the state $1–1.5 billion

Impacts of irrigation

  • In addition to salinization, there are various impacts of irrigation:

    • Loss of aquifer capacity 

      • This is caused by diesel-run machinery, which abstracts water faster than the aquifer is recharged

    • In the state of Texas, irrigation has reduced the water table by 50 metres

    • Irrigation has reduced the world’s albedo by 10% because dark green surfaces replace sandy surfaces

    • Evapotranspiration rates increase in the summer when surfaces have been irrigated 

    • Hailstorms and tornadoes can increase over irrigated areas due to an increase in the moisture in the soil, which results in more evapotranspiration

Case Study: France

Stakeholders

  • There are a number of stakeholders who may be affected by changes in water scarcity and quality, including:

    • Governments trying to achieve food security

    • Water companies that need to supply clean water to consumers

    • Farmers 

    • Domestic consumers who rely on clean water supplies

    • HEP companies 

    • Environmental groups

    • Industry 

Water scarcity and quality in France

  • The OECD reported in 2020 that agriculture is responsible for 11% of total freshwater abstractions in France

    • In summer, this percentage increases significantly

  • Agricultural pollutants are putting pressure on surface waters

  • France is part of the European Union (EU) and so has to follow EU laws, which include

    • Three main directives which have frameworks and standards to try and reduce agricultural pollution

    • The 2006 Water and Aquatic Environment Act 

  • Agriculture in France is now subject to three fees

    • A fee for the potential spread of agricultural pollution 

    • A charge to distributors of fertilisers and pesticides 

      • The higher the charge, the more toxic the product is

    • A fee for water pollution caused by livestock breeding

    • EU law also states that farmers in France must obtain water permits to abstract water for farming

    • The EU has banned some types of fertilisers which affect aquatic life

  • Farmers in France suffer water shortages, which has affected agricultural production

    • In some areas, yields fell by as much as 50%

  • In 2022, France’s reservoirs were 80% below normal levels

  • French authorities argued that giant irrigation reservoirs are necessary to support French farmers

  • French farmers have been using precision farming, which is when farmers observe and manage their farms through the use of Geographic Information Systems (GIS)

    • Through precision farming, the farmers can reduce their water consumption and fertiliser and pesticide use on the farms

    • Precision farming also enables the farmer to help prevent the leaching of fertilisers and pesticides into the soil, which could ‘run-off’ into rivers

  • Farmers have been using drip irrigation systems to administer the specific amount of water that is needed for good crop production

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