Environmental impacts of agriculture

• Farmland clears large areas of land where climate is favourable and the soil is fertile.
• Drainage in agriculture can cause habitat impacts. Farmland is often drained to produce more aerobic soils. Wetland species and the animals they support may not be able to survive the changes.
• Nutrient enrichment in agriculture can have habitat impacts. Using fertilisers increases nutrient availability and plant growth rates. Species that respond by growing taller such as grasses may out-compete smaller plants, such as wildflower species.
• Reduced biodiversity in agriculture can cause habitat damage. Natural ecosystems often have small-scale local variations in abiotic factors producing differences in the composition of the community of species found there. Agroecosytems often replace diverse communities of native species with a community of species that has fewer species, many of which may not be native. Many native species will not be able to survive the new conditions or may be removed because they are predators or competitors.
• Agriculture can create new habitats, such as hedgerows, which may be gradually colonised by wildlife species.
• Agricultural systems often introduce species into areas. Some crop and livestock species colonise surrounding areas and become pests; some are accidentally introduced pests; introduced predators to reduce pest populations could also reduce populations of non-target species.
• Pesticides can cause pollution. Pesticides are deliberately used because they are toxic, and are intended to kill pests, but they are not species-specific, so sensitive non-target species may be killed. Species may also be affected if inter-species relationships are affected such as the death of food species or pollinators.
• Nutrient pollution can cause pollution. The nutrients that were intended to stimulate crop growth, or are digestive wastes from livestock, can stimulate the growth of undesirable organisms. Leached inorganic nutrients cause eutrophication. Organic nutrients can cause deoxygenation of rivers and lakes because of the aerobic respiration of bacteria.
• Nitrate toxicity can cause pollution. Nitrates can be leached from farmland into water bodies that are used as sources of potable water for human consumption. High nitrate levels can cause methaemoglobinaemia and nitrates may be a human carcinogen.
• Climate change can cause pollution. Carbon dioxide is released during fossil fuel use and ploughing increase soil aerobic respiration; methane is released through livestock intestines, rice padi fields and microbial anaerobic digestion; oxides of nitrogen from livestock manure and nitrogen fertilisers.
• Embodied energy can cause pollution. The manufacture of materials, especially nitrate fertilisers and machinery, usually involves the use of fossil fuels and causes the release of GHGs.
• Agriculture has caused changes in the hydrological cycle. Irrigation water can deplete the sources of water; soil erosion caused by agriculture can reduce the effect that soil has on the hydrological cycle; soil compaction can increase runoff rates and cause more rapid fluctuations in river flow; agriculture changes evapotranspiration rates.
• Soil erosion is a natural process but poor soil management can lead to the rate of erosion exceeding the rate of formation, so the amount of soil present declines.