We rely on the land to provide the country with food, mineral1 resources and places to build our homes and industries, but all these uses can put a strain on the land and affect the soil itself.
Farming
New Zealand relies on farming to provide the food we eat and to provide the country with an income from exports. We have many important crops, such as apples, kiwifruit, and grapes (for wine). We grow cattle for beef and for milk products, and sheep for meat and wool. But much of New Zealand’s farmland has low nutrient2 soil. Farmers add fertiliser to improve the fertility of the land and therefore increase production. The use of fertilisers3 has been increasing over the years, especially with the increase of dairy farming on land once considered unsuitable. The problem is that often farmers apply more fertiliser4 than can be used by the crop5 or grass, and the excess washes off into our waterways. These nutrients6 can then cause aquatic7 plants to grow more quickly than they normally would. This rapid growth uses up all the oxygen8 in the water, and because there is less oxygen in the water, the animals that live in the streams and rivers may die. It can also increase the amount of nitrates in our drinking water, which is linked to a potentially fatal disease9 in infants called methemoglobinemia10 or ‘blue baby syndrome’.
Crop pesticide
Pesticides are commonly used in agriculture to prevent disease and improve yields. We are discovering that many pesticides used are hazardous to the environment. Many of these chemicals are no longer used, but some are still in use today. It is important for scientists to establish the long-term risk of these chemicals to our health and the health of the environment.
The use of pesticides11 has also been increasing in New Zealand. The ability of a chemical to get into the water depends on how easily it breaks down, the ability to dissolve in water, the type of soil it is applied to and how much the pesticide12 is used. A study conducted in the Waikato region measured the levels of pesticide in groundwater13 in areas where pesticides were regularly used. Of 35 wells measured, 20 had traces of pesticide. Almost all of these had levels well below the maximum accepted values (MAV) set for our drinking water. Two wells contained levels of the pesticide (dieldrin) that were much higher than the MAV. This insecticide14 was believed to have come from nearby sheep-dipping pits.
Sheep dipping is carried out by farmers to control15 insects on the animals. In the past, this involved dunking the sheep into a pit of organochloride insecticides, such as dieldrin, lindane or DDT16. Arsenic17 was also used as a dip before the 1950s. The use of organochlorides for sheep dipping stopped in the 1970s, so the results described above highlight the long-lasting nature of this toxin18. New Zealand has up to 50,000 old sheep dips, and many of them are likely to be considered contaminated sites.
Industry
Many industries use chemicals19 in their production processes. Often, in the past, these chemicals were not used or stored in ways that would be deemed safe by today’s standards. People were not so aware of the harm these chemicals could do to our health or our environment as we are today. Today, we have to abide by laws that enforce proper use and storage of chemicals.
Kinleith Mill
Kinleith Mill is a paper and pulp mill in the Waikato region of New Zealand. Chemicals are often used as part of the process in breaking down the wood into the fibre that is used to make paper. In the past, we weren’t aware of the harm these chemicals can have on the environment. Now, there are laws and guidelines in place to restrict the use of some chemicals and to ensure the chemicals we do use are disposed of safely.
One industry that uses chemicals is timber treatment. Preservatives are added to wood to prevent the timber being attacked by fungi20 and insects. One of these chemicals was pentachlorophenol (PCP), which was later banned in 1991. There are still several timber treatment sites that are considered to be contaminated.
Natural soil pollutants
New Zealand has traces of several heavy metals21 in its rocks that can become pollutants. We have many geothermal22 hot springs, which can form deposits of heavy metals such as arsenic, mercurycadmium, zinc and lead.
Arsenic is the most commonly occurring potential natural toxin in our environment. Arsenic can get into the soil through weathering23 and erosion24 of rocks or by leaching25 into groundwater. Arsenic is a highly toxic26 carcinogen27, which can cause bladder, kidney and liver28 cancer29. It may also affect the nervous system and cause birth defects.
Processes such as gold mining can increase the level of heavy metals in the environment, as gold30 is commonly found with other heavy metals that are left behind when the gold is extracted.
Related activities
Find out more about soil quality by conducting a visual soil assessment to examine soil structure31 and look for earthworms.
Use this web quest activity to get groups of students using web links provided to study the clean-up of sites contaminated by hazardous32 waste.
Explore the issues of land use and water quality with nutrient pollution and water and nutrient leaching. These demonstrate how nutrients enter into water systems or use an aquarium nitrate33 test kit to test water samples.
Combine science learning with ethical issues and explore the balance between farming and environmental tensions.
Related content
Find out more about soil formation, soil properties and soil contamination.
Tupuānuku is a whetū34 in the Matariki35 cluster. This article uses Tupuānuku as the context for reporting on soil quality and soil losses in Aotearoa36, with links to mātauranga Māori37.
- mineral: 1. (Geology) A naturally occurring solid formed through geological processes. Any given mineral has a characteristic chemical composition and a specific set of physical properties. 2. (Dietary) An inorganic compound needed for proper body function and maintenance of health, for example, iron in the form of haeme present in red meat.
- nutrient: A substance that provides nourishment for growth or metabolism.
- fertiliser: Compounds that are given to plants to promote growth.
- fertiliser: Compounds that are given to plants to promote growth.
- crop: 1. In agriculture, a cultivated plant that is grown on a large, commercial scale. The term most often refers to cereals, fruits and vegetables. 2. A compartment of muscle tissue that birds use to store and soften their food before it moves on to be processed by the gizzard.
- nutrient: A substance that provides nourishment for growth or metabolism.
- aquatic: Growing or living in or near water (either freshwater or marine).
- oxygen: A non-metal – symbol O, atomic number 8. Oxygen is a gas found in the air. It is needed for aerobic cellular respiration in cells.
- diseases: 1. An abnormal condition of an organism that impairs bodily functions. 2. In plants, an abnormal condition that interferes with vital physiological processes.
- methemoglobinemia: A disease in babies where their blood is unable to carry enough oxygen. It can be caused by excessive nitrates, often from fertilisers, in drinking water.
- pesticide: A substance or mixture of substances intended to repel, prevent or destroy plant, fungal or animal pests.
- pesticide: A substance or mixture of substances intended to repel, prevent or destroy plant, fungal or animal pests.
- groundwater: Water located beneath the Earth’s surface in soil spaces and in fractures of rocks.
- insecticide: A chemical (synthetic or organic) used to kill or repel insects.
- control: 1. Part of a scientific experiment in which no treatment has been applied in order to see whether there are any detectable differences to the experiment that did receive a treatment. 2. To hold in check or to curb.
- DDT: Dichlorodiphenyltrichloroethane. An insecticide used by farmers in the 1950's to kill pests like grass grubs. It is toxic to humans and other mammals when it is swallowed or absorbed through the skin.
- arsenic: A naturally occurring element that is highly toxic to most organisms.
- toxin: A poisonous substance that is a specific product of the metabolic activities of a living organism.
- chemicals: Everything is made up of chemicals. All matter (anything made of atoms) can be called chemicals. They can be in any form – liquid, solid or gas. Chemicals can be a pure substance or a mixture.
- fungi: The Fungi are a kingdom separate from plants and animals. Like animals, a fungus (or fungi – plural) is an organism that cannot make its own food. It can be multicellular such as mushrooms and moulds, or unicellular such as yeasts. Fungi may be decomposers, parasites, or mutualists (helping plants to grow).
- heavy metals: Elements that exhibit metallic properties. Often refers to toxic heavy metals that can cause serious illness in organisms. Waste-derived fuels are especially prone to containing toxic heavy metals.
- geothermal: Geothermal energy is energy produced from the heat of the Earth.
- weathering: Chemical, mechanical (including freezing and thawing) and biological processes that break down rocks into smaller pieces. Weathering does not include the transport away of broken-down material.
- erosion: Wearing away of the land by mechanical action, such as by wind, water and glaciers, and by material carried in them. It can also be the gradual wearing away of a surface due to friction, particle collisions or chemical attack. Part of the process of erosion transports material away.
- leaching: When a compound becomes dissolved in water and moves from one place to another, for example, a fertiliser in the soil dissolves in rain water and ends up in a stream.
- toxic: Poisonous and harmful.
- carcinogen: A substance that can cause cancer.
- liver: A vital organ situated beside the stomach. It is the body’s largest internal organ and plays a major role in metabolism as well as other important and complex functions.
- cancer: The term for a group of more than 100 diseases in which abnormal cells divide and multiply uncontrollably.
- gold: A transition metal in Group 11 of the periodic table – symbol Au, atomic number 79.
- soil structure: The way that soil particles are arranged together.
- hazardous: A situation that poses a level of threat to life, health or the environment.
- nitrate: A chemical composed of three oxygen atoms for every nitrogen atom.
- whetū: Māori word for star.
- Matariki: A star cluster that appears in the early morning sky for the first time in the year in late May or June. It marks the beginning of the Māori New Year.
- Aotearoa: The Māori name for New Zealand, meaning Land of the Long White Cloud.
- mātauranga Māori: A contemporary term referring to Māori knowledge, Māori ways of knowing and associated practice.
