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

• 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