Agriculture and Environment: Wheat

Environmental Impacts of Production: Water Use & Pollution

There are several impacts of wheat production on water resources.

First, because many countries see wheat as a strategic food crop and want to be self-sufficient in basic food production, the crop is often grown in areas with insufficient rainfall to support it. Wheat is the second most irrigated crop cultivated globally.

Soil salinisation, water contamination
Irrigation always brings with it the problem of soil salinisation, which at low levels reduces yields but eventually can make soils unfit for any type of cultivation. In addition, pollution of waterways with silt from soil erosion, surface water pollution due to agrochemical runoff, and subsurface contamination of aquifers due to agrochemicals are all problems that can be caused by the production of wheat.

Altering drainage and hydrology
Wheat production can also affect the amount of water available for agriculture or other uses, both indirectly through changes in hydrology and directly through diversion for irrigation. Habitat conversion for wheat cultivation often causes severe changes in the drainage and hydrology of vast areas.

In natural landscapes the organic matter on the surface and within the soil acts like a sponge. Water is absorbed and released over time. After conversion to wheat, water runoff is more seasonal with severe peaks and valleys in runoff rates. Irrigation of wheat can cause major changes in ecological structures of landscapes such as reduced water flow or even the elimination of streams, rivers, wetlands, or marshes.

Depleting underwater reserves
Changing the course and speed of water flows, along with seasonal changes in water levels, can devastate plants, animals, and fish. Underground water resources can also be depleted by pumping water for irrigation, especially when those are non-renewable sources such as ossified aquifers. This causes tremendous problems for people who depend on those underwater reserves as their water source.

Imbalances in Biochemical Oxygen Demand
Water quality is another important issue. Runoff from grain fields pollutes surface water with nutrients such as nitrogen and phosphorous as well as particulates (silt). Phosphorous in particular tends to be a problem because it feeds algae and can cause algal populations to explode.

Huge quantities of algae can deplete the oxygen in creeks, rivers, ponds, and lakes, creating excessive biochemical oxygen demand (BOD) and killing fish and other aquatic life. This starts a process known as eutrophication, which can permanently alter water bodies. Organic matter carried in runoff from grain fields also increases the BOD of surface waters. Groundwater quality can also be affected through the leaching of fertiliser nutrients and other agricultural chemicals into underground water sources.

Linked to skin diseases and cancers
The health impacts of water quality changes from agriculture, for humans and other species, are only beginning to be investigated. Groundwater contamination from nitrates in fertilisers has been linked to methemoglobinemia or "blue baby syndrome." Groundwater contamination from pesticide residues has been linked to such human ailments as skin diseases, autoimmune diseases, and some cancers. The evidence on pesticide residues for humans is fragmentary, however, and even less research has been done on other species.

Some research is beginning to indicate that pesticides have demonstrated carcinogenic and teratogenic properties (causing birth defects) in animals, even though few have been shown to be cancer-causing in humans (Cabello et al. 2001; Reif 1999). Other studies have shown a correlation between pesticide exposure and certain types of cancer in some populations of agriculture workers (Mills 1998).

Posing risks to wildlife species
Runoff from wheat fields is often funnelled through a very small number of rivers, where the aggregate impact of even small quantities of chemicals over such a large area can be significant. Reports, for example, have suggested that pesticides used on wheat have been linked to frog deformities in Minnesota.

However, controlled experiments found correlations between prior infections by trematodes (parasitic flatworms) in frogs and common pesticides such as atrazine (the most commonly used herbicide in North America), malathion (used to control both household and agricultural insect pests), and esfenvalerate (a synthetic pyrethroid insecticide) (Associated Press 1998; Danielson 2002; Milwaukee Journal Sentinel 1999). Although atrazine is not used in wheat production, these pesticides can become mixes in common water bodies and can have cumulative interactive effects.