What causes farm pollution, how is eutrophication caused, and how can farmers reduce pollution and reuse waste?
The main sources of farm pollution, the Nitrates Directive and Nitrate Vulnerable Zones, eutrophication using Lough Neagh, how farmers reduce pollution including technology, water quality using BOD and indicator species, and energy from anaerobic digestion.
A focused CCEA GCSE Agriculture and Land Use answer on pollution and farm waste, covering the sources of farm pollution, the Nitrates Directive and Nitrate Vulnerable Zones, eutrophication of Lough Neagh, reducing pollution including technology, water quality using BOD and indicator species, and anaerobic digestion.
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What this dot point is asking
CCEA wants you to identify the sources of farm pollution, explain the Nitrates Directive and Nitrate Vulnerable Zones, explain eutrophication using Lough Neagh, describe how farmers reduce pollution (including technology), assess water quality using BOD and indicator species, and explain energy from anaerobic digestion.
Sources of farm pollution
The Nitrates Directive and Nitrate Vulnerable Zones
These rules set closed periods when slurry cannot be spread and limits on application, protecting rivers, lakes and groundwater.
Eutrophication (Lough Neagh)
Reducing pollution and using technology
Farmers reduce pollution from animal waste and effluent by:
- Careful slurry application using a dribble bar or shallow injection rather than splash-plate spreading.
- Dirty water irrigation to use, not waste, dirty water.
- Reed beds, which clean dirty water naturally.
- GPS on tractors, allowing accurate application of fertilisers and pesticides so less is wasted and less pollutes.
Assessing water quality: BOD and indicator species
Clean-water indicator species include mayfly nymphs, stonefly/damselfly nymphs, caddis fly larvae and dragonfly nymphs; finding them shows clean water, while their absence shows pollution.
Anaerobic digestion
Farms can produce energy from anaerobic digestion: animal waste (slurry) is broken down by microorganisms without oxygen in a digester, producing biogas that can be burned for heat or electricity, while the leftover material can be used as fertiliser. This turns a waste and pollution problem into a renewable energy source.
Examples in context
Example 1. A reed bed for dirty water. A farmer builds a reed bed to treat dirty yard water before it reaches a stream. The reeds and the microbes around their roots remove pollutants naturally, so cleaner water leaves the farm, reducing pollution at low running cost, although the reed bed takes up space and must be maintained.
Example 2. An anaerobic digester on a dairy farm. A dairy farmer feeds slurry into an anaerobic digester, which produces biogas burned to generate electricity for the farm, and a residue used as fertiliser. This reduces the pollution risk from storing slurry, cuts the farm's energy bills and emissions, and turns waste into a useful product.
Try this
Q1. Name three sources of farm pollution. [3 marks]
- Cue. Any three: silage effluent, excess fertiliser and animal waste, air pollution from slurry, noise from machinery, dirty yard water.
Q2. State what a high biological oxygen demand (BOD) tells you about water. [1 mark]
- Cue. It indicates more organic pollution, with microbes using up the oxygen.
Exam-style practice questions
Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
CCEA Unit 2 style6 marksUsing Lough Neagh as an example, explain how eutrophication is caused and what its effects are.Show worked answer →
Marks for the cause, the sequence and the effects.
Eutrophication is the enrichment of water with nutrients, especially nitrates and phosphates. At Lough Neagh it is caused mainly by the over application of fertilisers and the run-off of animal waste from farms, which wash nutrients into the water.
The sequence: the extra nutrients cause rapid growth of algae (an algal bloom) on the surface. This blocks light from plants below, which die. Bacteria then decompose the dead algae and plants, and this decomposition uses up the oxygen dissolved in the water.
The effect: with little oxygen left, fish and other aquatic animals cannot respire and die. The water quality falls and the ecosystem is damaged.
Markers reward the nutrient cause (fertiliser and animal waste), the ordered process (algal growth, light blocked, decomposition, oxygen used up) and the consequence of fish death.
CCEA Unit 2 style4 marksExplain how indicator species and biological oxygen demand (BOD) can be used to assess water pollution.Show worked answer →
Two marks for indicator species and two for BOD.
An indicator species is a species whose presence or absence tells you about the conditions, in this case how clean or polluted the water is. Some invertebrates, such as mayfly nymphs, need clean, well-oxygenated water, so finding them shows clean water; if only pollution-tolerant species are present and the clean-water species are gone, the water is polluted.
Biological oxygen demand (BOD) is the amount of oxygen used by microorganisms as they break down organic matter in the water. A high BOD means a lot of organic pollution, because the microbes are using up a lot of oxygen, leaving less for fish and other animals. So a high BOD indicates more polluted water.
Markers reward the idea that clean-water indicator species (e.g. mayfly nymphs) show clean water, and that a high BOD shows more organic pollution and lower oxygen.
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