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Chapter 12 Effects of Agriculture on the Environment Many environmental problems result from agriculture: • Soil erosion • Sediment transport and deposition downstream • On-site pollution from fertilizers and pesticides • Deforestation • Desertification • Degradation of water aquifers • Salinization • Accumulation of toxic metals and organic compounds • Loss of biodiversity Our Eroding Soils • U.S. - 1/3 of country’s topsoil lost – 1930’s and post WWII • Loses fertility QuickTime™ and a BMP decompressor are needed to see this picture. – Increased sunlight – Warms soil and speeds up organic decomposition • Rate of loss of fertility – Time required for soil to lose 1/2 of its original store of the chemical elements necessary for crops • Erosion today still greater than soil regeneration Where Eroded Soil Goes: Sediments Also Cause Environmental Problems QuickTime™ and a BMP decompressor are needed to see this picture. *Sediments choke fisheries and coral reefs *Chemical effects: nitrates, ammonia and other fertilizers cause lake eutrophication * Although erosion has decreased, still greater than the rate of soil regeneration Where Eroded Soil Goes: Sediments Also Cause Environmental Problems Ways to slow erosion: • Making Soil Sustainable • Contour Plowing (most effective in recent years) • No-Till Agriculture – Combination of farming practices that include not plowing the land and using herbicides to keep down weeds. Controlling Pests • Insects • Nematodes • Bacterial and viral diseases • Vertebrates • Weeds (major problem) – Compete for resources, light, water, nutrients and space QuickTime™ and a BMP decompressor are needed to see this picture. History of Pesticides • Removal or use farming methods to decrease • Chemicals – Narrow-spectrum pesticide – Broad-spectrum pesticide • Petroleum-based sprays and natural plant chemicals • Artificial compounds (DDT) • Biological control – Predators, parasites and competitors DDT • Malaria • Ideal pesticide – – – – No short-term effect on people Seemed to only kill inects Relatively insoluble in water Believed transportation not hazardous • Long-term effects – – – – Egg production (predatory bird) Possible increase in cancer in humans Biomagnification Storage in fats/oils allows to be transferred biologically Integrated Pest Management – Control of agricultural pests (rather than complete elimination) using several methods together, including biological and chemical agents • No or low-till agriculture • Spatial complexity and biological diversity • Less damaging – Goals: • To minimize the use of artificial chemicals • To prevent or slow the buildup of resistance by pests to chemical pesticides Monitoring Pesticides in the Environment • Decompose in place • Transported – Wind, surface and subsurface waters • Sometimes initial product breakdown is toxic (DDT) or takes a long-time to become non-toxic – No well established program – Must monitor concentrations • Public and environmental health standards Genetically Modified Crops • “Novel” changes – Do not occur in nature; are more likely to have negative effects • Can apply this rule to three categories of genetically engineered crops – New hybrids – Terminator gene – Transfer of genes New Hybrids • Occurs naturally • Increase in agricultural productivity • Concerns: – Superhybrids – Superweeds – Marginal lands The Terminator Gene • A genetically modified crop which has a gene to cause the plant to become sterile after the first year • In theory, the gene prevents genetically modified crops from spreading • Protected “corporately” • Poor nations Transfer of Genes • “Novel” effect • Can lead to unforeseen and undesirable environmental effects – Potatoes and corn – Caterpillars – Monarch butterflies QuickTime™ and a BMP decompressor are needed to see this picture. Grazing on Rangelands • Overgrazing occurs when the carrying capacity is exceeded. It can cause severe damage to lands. – – – – Trampling stream banks; animal waste Slows vegetation growth Reduces plant diversity Leads to dominance by plant species undesirable to cattle – Hastens soil erosion as plant cover decreases Grazing on Rangelands • It is important to properly manage livestock, including using appropriate lands for grazing and keeping livestock at a sustainable density – Density related to rainfall amounts QuickTime™ and a BMP decompressor are needed to see this picture. Biogeography of Agricultural Animals • Domestic animals introduced into new habitats – Native vegetation not adapted to introduced grazers; may be greatly reduced and threatened with extinction – Introduced animals may compete with native herbivores, reducing their numbers – Ex: Tropical rainforest to rangeland Desertification • Affects 1/6 of the world’s population (largest part in poorest countries) • Desertification is the deterioration of land in arid, semi- arid and dry sub humid areas due to changes in climate and human activities • Can be caused by – – – – Poor farming practices Conversion of marginal grazing lands to croplands Poor forestry practices Soil contamination Symptoms of Desertification • • • • Lowering of the water table (deeper wells) Increase in salt contamination of the soil Reduced surface water (streams, ponds) Increased soil erosion (dry soil blown and washed away) • Loss of native vegetation (not having adapted to desert conditions, native begetation can no longer survive) Rice in Dry Climates QuickTime™ and a BMP decompressor are needed to see this picture. • California • Biggest water users in the state • High pesticide and herbicide use • Air pollution • Salmon • Wetland habitat • Waterfowl migratory route