Livestock farming and air quality

Globally, the main source of greenhouse gas emissions comes from the burning of fossil fuels, such as oil. But in New Zealand the main source comes from farmed animals.

Cattle, sheep and other domestic stock produced about 40 pe rcent of New Zealand’s total greenhouse gases in 1998. The remaining 60 per cent came from sources such as industry, transport and household emissions.

The main greenhouse gases are carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), and chlorofluorocarbons (CFCs).

Livestock farming produces:

• methane – produced when animals digest their food
• nitrous oxide – produced when animal urine reacts with soil.

Human-made sources of methane include:

• emissions of natural gas
• decomposing waste in landfills
• coal mining.

An assessment of natural sources of methane in the Waikato region in 1998 found that about:

• 90 per cent was produced by farmed animals
• 7 per cent in total was produced by:
  
  • vegetation - native and exotic
  • land - including urban areas
  • waterways and coastal areas
• 2 percent was produced by geothermal power stations and natural geothermal areas.

Methane and livestock

Methane is produced by ruminants, such as cattle, sheep, goats and deer. Ruminants rely on bacteria present in their rumen (first stomach) to digest their highly fibrous diet. Methane is a by-product of this kind of digestion.

Of the farmed ruminants, cattle generate the highest emissions of methane (CH₄). Wild animals such as possums are likely to emit only a fraction of the total farmed animal emissions.

The Waikato region contains about 50 per cent of New Zealand’s peatlands. Waikato peatlands cover approximately 94,000 ha and contain about 2,700 million cubic metres of peat.

Peat forms from the build up of partially rotted plant material in wet environments. This partly rotted material contains a large amount of carbon. It’s been estimated that Waikato peatlands contain about 76 million tonnes of carbon.

When peat is drained for development or to create pasture, the carbon in peat becomes exposed to air. The carbon is then able to bind with oxygen (O₂) in the air to form carbon dioxide gas (CO₂) (oxidation). It is estimated that developed peatland releases about 1.4 million tonnes of carbon dioxide each year (in comparison, transportation produces around 2 million tonnes annually).