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
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