Environmental impacts of Agriculture

Freshwater 

Freshwater is vital for farming as it drives both plant and animal production.  Plant production depends on an adequate water supply, and animals require plants as a food source.  In the drier regions of New Zealand, such as Canterbury, Marlborough and Central Otago, agricultural production is dependent on water from irrigators. In regions not previously thought to be water-short, irrigation may be needed at strategic times or in relatively dry seasons, in order to ensure reliable crop/animal production, particularly given impacts of climate change. See the climate change section here. 

Each year, farmers make significant on-farm investments in order to optimise their use of water and reduce their overall impact on the quality and quantity of waterways and waterbodies. These investments include improvements in irrigation system efficiency, effluent management (including effluent storage systems), riparian management and staff education and training.  There is still a lot more work to ensure all New Zealand freshwater is of a suitable quality and quantity.

Irrigation 

The development of reliable irrigation has large economic and community benefits, which have been clearly demonstrated by flow-on economic developments from the Opuha dam in South Canterbury 4893  and from the North Otago Irrigation Scheme. 4894

Since the late 1970s, irrigated farmland in New Zealand has doubled in area every 12 years. There is currently around 720,000 hectares 4895 of irrigation in New Zealand, which is about 6% of total New Zealand farmland.  This irrigated land produces $2 billion (net) at farmgate, or 20% of total agricultural GDP. 4896  

Irrigated farmland typically generates three times the production of an equivalent area farmed under dry-land systems.  IrrigationNZ advises that for every $1 of wealth created on an irrigated farm at least another $3 is created in the wider rural and urban communities.

Reliability of supply (water storage) is essential for efficient irrigation. However, strategic management of the water resource is required to ensure the opportunities irrigated agriculture can offer are maximised in a sustainable manner, safeguarding the values of the many diverse stakeholder interests.Reliable and secure water supply combined with well-managed irrigation practices are key to ensuring good environmental outcomes.

The growth of irrigation in certain areas of the country is due to a desire to sustain and intensify farming enterprises in areas which climatic conditions are highly variable and summer conditions can be extremely dry.

Dairy farming also tends to use a lot of water compared to other types of farming – in a 2004 Taupo study, dairy farming was found to use on average 83,000 litres per day whereas drystock farms used 14,000 litres per day. This meant that at that time, dairy farms were using six times more water per hectare than drystock farms. 4897

Under low flow conditions, peak demand which is mainly for irrigation, cannot either be met by current abstraction methods or sustain the current methods of use. Methods to store surface water from lakes and rivers need to be found if the resource managers are to keep up with demand. However, suitable places to store water are few and far between, as they generally require the flooding of land. This is often land which has other important uses and environmental values. The impact of intensification on water quality must also be considered.

Point source pollution 

Point source pollution has generally declined over the last 20 to 30 years as treatment system technology has been upgraded, and alternative methods of disposal have been developed, including applying effluent to land rather than discharging it into waterways. Progressively stricter controls on discharge practices were introduced under a 1971 amendment to the Water and Soil Conservation Act 1967 and subsequently under the Resource Management Act 1991. Under most New Zealand regional and district plans, point source pollution from agricultural activity is now prohibited.

Meatworks, dairy factories, tanneries,fertiliser plants, stockyards and many other types of agricultural enterprise pose a risk of discharging pollutants into the catchment. In the early years of Europeansettlementthere were many such enterprises scattered across the country, all discharging industrial or agricultural waste on a small scale. However in the last 30 years agricultural and industrial activity has changed, so that there are numerous larger operations. For example, in 1970 there were more than 200 dairy factories whereas there are now only about 30. 4898  These bigger businesses tend to be better able to deal with waste effectively because of their relative financial strength and access to technology. Furthermore, the last 30 years have seen the implementation of stricter legal requirements and a shift in attitudes towards greater recognition of the importance of avoiding pollution, together with a greater interest in finding better technology to achieve this.

Whereas historically farmers may have discharged effluent from dairy sheds directly into waterways, this is now prohibited. They are now required to use pond treatment systems or land irrigation systems to dispose of effluent. Two-pond treatment systems pass the effluent through two ponds, each containing different naturally occurring types of bacteria, before discharging it into the catchment. This system can remove up to 95 per cent of the organic matter from the effluent. HowTo be effective, the ponds need to be well designed and maintained and adequate for the herd size, and DairyNZ’s new Warrant of Fitness programme has an objective to ensure all dairy farmers in New Zealand have suitable and appropriate effluent management systems in place. New technology is also being developed which may enable energy from wastewater solids, and algae grown on wastewater nutrients, to be harvested as biogas. 4899

Land irrigation disposes ofwaste waterand nutrients to fields or forest rather than into the water. Soils have differing potentials to deal with nutrients, both seasonally and through their nature. Land disposal is effective in protecting the catchment from pollution so long as the land is not overloaded. At this point nutrients will wash off into streams or leach into the groundwater, posing the same risk to the ecosystem as they would have if they had been discharged directly into waterways. 4900  As a result, Regional Council water plans generally now prohibit the ponding of effluent via such irrigation to land.

Non-point source pollution 

Whilst pollution from point sources has been decreasing over the last few decades, focus is now on reducing non-point source agricultural pollution. Point sources now account for only 3.2% of the total nitrogen and 1.8% of the total phosphorus fluxes to the sea.  The universal diffuse pollutants: nutrients, fine sediments and pathogens which are all mobilised by livestock, predominate New Zealand waters. 4901 Diffuse, or non‐point source pollution, derives from a wide array of activities which involve no single distinct source, which makes it more difficult to manage with regulations.

Diffuse pollutants move into water through: overland runoff; direct access to waters by livestock, and leaching to groundwater. 4902 Agricultural runoff has been a problem for New Zealand’s waterways for many years. As native vegetation is turned into pasture, wetlands drained and stream bank vegetation removed, the land becomes less able to absorb water. As more water runs from the land to the waterways it picks up sediment, organic matter (effluent) and nutrients that are deposited on pasture, transferring them to the waterways.

In recent years the condition of many lowland streams in farming areas has deteriorated. This has been coupled with the widespread conversion of sheep farms and forestry to dairying (and less commonly, deer farming), and a trend towards intensification of dairy farming, taking advantage of improvements in fertilisers and stock management, so that more cows can be kept on a given piece of land.

Increasing pollution problems have brought about a growing awareness of the effects that agricultural activity can have on waterways. In recent years farmers have made efforts to resolve these problems, but improvements thus far have not managed to fully reverse the trend towards nutrient enrichment of lowland waterways. Nutrient pollution from runoff is increased where drains like mole and tile systems are used to dry out pasture-land. These work in clay soils and are common in Otago and Southland. They use perforated plastic tubing sunk at a depth of about 50 centimetres to carry water from pasture into larger drains.

Tunnels are also made at a slightly shallower depth, at about five metre intervals, by dragging a torpedo shaped device through the soil. This creates a network of small drains across the paddock that lead water into the plastic tubing. The system is effective at removing water from pasture, but it also has the potential to increase the amount of pollution that is transferred to the waterways.  Both Southland and Otago Regional Councils now have rules in place to regulate the effects of these activities.

Nutrient pollution, predominantly in the form of nitrogen and phosphorus, is one of the most significant by-products of agricultural activity. Nitrogen and phosphorus are essential parts of amino acids and nucleic acids, and consequently they are essential building blocks for all life on Earth. Unfortunately when they appear in waterways in excess they can be very harmful, because they disrupt natural processes of growth and decay. The nutrients can come from a number of sources. New Zealand’s livestock excrete nearly 40 times more organic waste than New Zealand’s human population. This is a large amount of organic effluent that must be disposed of. Nitrogen and phosphorus pollution is also derived from fertilisers which are applied to agricultural pasture to promote grass growth. The amount of nitrogen fertiliser used in New Zealand has continued to increase over the past two decades.

Recent work has also identified gorse as a potential contributor of nitrogen to waterways. A study which quantified nitrate leaching from stands of gorse growing in the Lake Rotorua catchment concluded that 43 tonnes of nitrogen per hectare derived from gorse were being leached into the groundwater each year. 4903

Non-point source pollution is a significant focus of the National Policy Statement for Freshwater Management 2014 which is explained in more detail elsewhere on this website, see here. The NPSFM 2014 directs regional councils, in consultation with their communities, to set objectives for the state of fresh water bodies in their regions and to set limits on both resource use and the discharge of contaminants to meet these objectives.  Farmers and primary industry representatives are a key part of these processes.  Local communities are coming together to work on plans for improving their local water resources. It is now accepted that everyone needs to play their part in protecting New Zealand’s freshwater resources.  Farmers are better understanding the relationship between what happens on their land and the waterways they rely upon. For many farmers and growers, this will mean a change of practice, to manage within the limits set. Industry groups are researching and working on education, support and innovation, guidance and field days to support this change of direction. 

Sedimentation 

The removal of hill and riparian forests for agricultural pasture increases the amount of rainfall running off the land into streams and rivers. The tree canopy in a mid-latitude forest typically intercepts and then evaporates away up to one third of the rain that falls on that canopy, effectively reducing the rain that reaches the ground. Canopy interception losses are a function of effective leaf area and canopy roughness, and in west coast locations with frequent rain, can be significantly greater than water losses to transpiration (water drawn up through the tree roots via photosynthesis). There is little difference in canopy interception losses between native and exotic forests, tall manuka and kanuka or dense infestations of gorse or broom, provided that a closed canopy exists.

But such interception losses are far greater than that occurring under tussock, short pasture grasses or crops. In contrast to the highly compacted soils often found under pastoral or arable agricultural systems, forest soils have much higher infiltration capacities and seldom generate overland flow or surface run-off. When forest is replaced by short-rooted pasture grass, increased amounts of rainfall are allowed to run off the land. In the absence of tree roots to hold the soil together, greater amounts of sediment made up of inorganic matter (rock and soil) and organic matter (mostly animal faeces), are washed from the land into groundwater, streams, rivers and wetlands.

Although most forest in New Zealand were removed between 800 and 80 years ago (in two waves with initial Maori impacts followed by extensive impacts of European settlement), the effects of these changes in the landscape continue to be felt, as the hills and riparian areas continue to be used for livestock production.

Pastoral catchments thus have a sediment load which can on average be two to five times greater than that of a forested catchment, 4904 except for the East Cape where major gully erosion that followed wholesale deforestation and establishment of exotic grasses has led to sediment yields of over a thousand times that of the original native forest cover. This excess sediment makes waterways muddy and murky. This is not only aesthetically displeasing but also makes the water less suitable for many native aquatic species and sport fish such as trout which need clear water for spawning and feeding.

The presence of large numbers of stock which churn up fields can exacerbate the problem. When farmers graze stock intensively on smaller fields during the winter, to minimise damage to valuable pasture, this can result in pugged (hoof damaged) bare soil with large amounts of effluent on the surface. Rainfall can wash this damaged topsoil and effluent into waterways. 4905 The effects of this are much worse when riparian areas are stripped of growth and used as pasture in addition to the main pasture area.

In recent years, most councils have now recognised this and either have setback rules requiring riparian buffer corridors or otherwise encourage or require  farmers to replant riparian areas, to ensure that a buffer zone is maintained between pasture used by stock and the waterway. 4906  

Removal of riparian shading

Most aquatic life in New Zealand’s waterways developed in heavily shaded forest conditions. When vegetation is removed from the banks of waterways, the amount of available shade is decreased so the temperature of the water increases, as does the growth of algae and aquatic weeds. Oxygen levels in the water also reduce as the temperature rises. This makes conditions for native aquatic life less than optimal. Riparian areas are also an important habitat for many types of native fauna, whose habitat may be destroyed by the removal of the vegetation.

The removal of trees from the riverbank can destabilise the area. Then allowing stock to graze the banks will exacerbate this problem. Removal of riparian planting also removes a valuable filter. Plants, leaf litter and soil can filter out sediment nutrients, faecal material and other pollutants that run off the land towards the waterway. In addition, undisturbed waterways and wetlands provide extremely valuable flood prevention control. Interfering with them reduces their ability to absorb and slow peak flows, and to release water slowly to maintain summer low flows. 4907

The requirement or encouragement through council plans to provide riparian planting and other buffers, and to ensure all lowland waterways are fenced will continue to ensure improvements in this regard.

Stock grazing 

Stock grazing in the areas around water bodies and in wetlands can contribute significantly to pollution. This is through direct nutrient enrichment and bacterial contamination of the water from faeces and urine damage vegetation. Stock can also decrease soil stability. Stock with access to waterways can contribute large amounts of faecal matter directly to the catchment. A study has shown that when cows cross a stream on their way to and from milking they are 50 times more likely to defecate in the water than on adjacent areas. 4908 As a result, a significant focus of current national and regional regulation, 4909 and dairy industry requirements such as the Water Accord) 4910 , are on keeping cows out of waterways and ensuring all waterways on intensively farmed land is fenced. 
 
The Clean Water package, a set of proposals announced on 23 February 2017, is the latest part of the reform programme. It includes:
  • a target that 90% percent of our rivers and lakes are swimmable by 2040;
  • greater information on our water quality for swimming;
  • proposals for changes to the National Policy Statement for Freshwater Management 2014;
  • details of proposals to exclude stock from waterways; and
  • the establishment of the $100 million Freshwater Improvement Fund. 

Stream modification 

Streams have historically been modified in order to increase the workable area of farms. Such modifications can include culverting or piping the stream as well as diversions and realignments of the stream bed. In Taranaki, a recent study estimated that over 700kilometresof streams had been modified within the region. 4911   These works can have significant impacts on freshwater bodies and result in habitat degradation and loss, reduction in water quality, changes in hydrological regime and loss of biodiversity. Council rules now manage or prohibit such modification.

Biodiversity 

The importance of biodiversity is explained in the biodiversity section of this website. Biodiversity means the variety of living things including plants, animals, insects or microorganisms. Biodiversity contributes to farming by assisting production in different ways. For example:

  • birds and spiders feed on pest insects which keeps pasture healthier;
  • earthworms cultivate and enrich the soil helping to produce higher pasture yields; and 
  • bees pollinate clover flowers and increase clover coverage. 

Agricultural threats to biodiversity 

The most pressing issues facing the protection and restoration of native biodiversity on productive land are invasive weeds and pest animals accelerating land use change, and the high level of agro-chemical inputs. All of these are driving farmland towards a low diversity environment. While rural landowners also desire to achieve financial returns from their land, it is important that biodiversity on productive land is protected, because of the essential ecosystem services it provides. This is becomingly increasingly accepted by landowners, stakeholders and councils alike.

The greatest pressure on biodiversity is weeds and pests. Although there has been significant progress in the battle against introduced weeds and animals on productive land, the increasing rise in the number of invasive weed and animal species is still recognised as the major threat to biodiversity. 4914 The DOC Community Fund allocates approximately $4.6 million per year to community groups for priority conservation work. This funding is used for practical, on the ground projects to maintain and restore indigenous biodiversity. 

The expansion and intensification of agriculture is destroying habitats for indigenous species. 4912  Expansion of agriculture into previously forested areas causes a reduction in habitat. Habitat loss remains a primary cause of indigenous biodiversity decline. Such expansion can leave small pockets of isolated habitat and there is little ability for species to move between them. 

Poor land management practices, including increasing use of agro-chemical inputs 

Today, many farms are reliant upon the inputs of fertilisers, pesticides and herbicides to run a successful operation. The effects of agricultural chemical use can be long lasting. For example, the pesticide DDT was used by New Zealand farmers during the 1950s and 1960s, primarily to kill grass grub and porina caterpillars. Although its use on farmland was prohibited in 1970, high levels of DDT accumulated in the country’s soils during the years of heavy application. Many New Zealand soils still contain high levels of DDT.

The threat to biodiversity from the dependence on chemicals cannot be understated. The key issues arising from the use of toxic chemicals on productive land include:

  • Impacts on the hydrological cycle as toxins run off into the waterways and end up accumulating in the groundwater and marine environment
  • Pollution of the soil with the accumulation of heavy metals
  • Eradication of insects and beneficial pollinating species which are integral to productive land systems

Other agricultural practices can also have a direct impact on biodiversity. Grazing stock can cause significant damage to remaining tracts of native vegetation. They browse on native plant species, disturb the ground and the native species living beneath the surface, and release large amounts of pollutants into the soil and waterways.

 

  1. Harris, S.; Butcher, G.; Smith, W. 2006. The Opuha Dam: An ex post study of its impacts on the provincial economy and community.  Aoraki Development Trust.

  2. Waitaki Development Board, 2010: The Economic Benefit to the Community of the North Otago Irrigation Scheme, prepared by The Agribusiness Group

  3. StatisticsNZ 2012 – and http://irrigationnz.co.nz/knowledge-resources/irrigation-new-zealand/fast-facts/

  4. http://irrigationnz.co.nz/knowledge-resources/irrigation-new-zealand/fast-facts/

  5. Parliamentary Commissioner for the Environment, 2004, Growing for good: Intensive farming, sustainability and New Zealand’s environment, Parliamentary Commissioner for the Environment, Wellington, page 45. 

  6. www.biotechlearn.org.nz

  7. Craggs R, 2005, ‘Energy from wastewater treatment’, Water & Atmosphere 12(4), 20

  8. Ministry for the Environment, 1997, The state of New Zealand’s environment 1997, 42

  9. https://www.landcareresearch.co.nz/publications/researchpubs/Howard_williams_2013_Diffuse_pollution_and_freshwater_degradation.pdf, page 2

  10. https://www.landcareresearch.co.nz/publications/researchpubs/Howard_williams_2013_Diffuse_pollution_and_freshwater_degradation.pdf, page 2. 

  11. Environment Bay of Plenty, 2010, Quantification of nitrogen leaching from gorse in the Lake Rotorua catchment, Environment Bay of Plenty Regional Council, Whakatane, available at http://envbop.govt.nz/Reports/EnvReport-201003-QuantificationNitrogenLeachingGorse.pdf

  12. Ministry for the Environment, 1997, Environment New Zealand 2007, 7.40

  13. http://www.es.govt.nz/environment/land/land-sustainability/grazing-winter-crops.aspx

  14. See for example: http://www.trc.govt.nz/publications/regional+plans/guidelines/farming/MARGINS.HTM

  15. http://www.trc.govt.nz/dairying/

  16. Ministry for the Environment, 2007, Environment New Zealand 2007, page 287

  17. http://www.mfe.govt.nz/publications/fresh-water/clean-water-90-of-rivers-and-lakes-swimmable-2040

  18. https://www.dairynz.co.nz/environment/in-your-region/sustainable-dairying-water-accord/

  19. Taranaki Regional Council, 2010, Small stream modification in Taranaki: An assessment of the ecological and hydrological values of small streams, the cumulative extent and ecological effects of modification, and implications for policy and practice, Taranaki Regional Council, Stratford, 35

  20. Lee W G, C D Meurk and B D Clarkson, 2008, ‘Agricultural intensification: Whither indigenous biodiversity?’, New Zealand Journal of Agricultural Research, 51(4), 457-460

  21. Marie Brown (2016) Pathways to Prosperity: Safeguarding biodiversity in development

  22. Green W and B Clarkson, 2005, Turning the tide? A review of the first five years of the New Zealand Biodiversity Strategy, The Synthesis Report submitted to the Biodiversity Chief Executives in November 2005, Wellington

Last updated at 2:43PM on February 19, 2018