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Environmental Science Unit 4: Land and water use

How people farm, build and harvest resources changes land and water. Sustainable practices reduce the damage.

Covers: Agriculture and the Green Revolution, irrigation, pesticides, tragedy of the commons, forestry, mining, urbanization, fishing

Study guide

Agriculture feeds the world but has major environmental costs. The Green Revolution increased yields with high-yield crop varieties, synthetic fertilizers, irrigation, pesticides and mechanization, but brought soil degradation, water pollution and dependence on fossil fuels. Monocultures (single crops over large areas) are efficient but vulnerable to pests and disease and reduce biodiversity. Sustainable practices include crop rotation, contour plowing, terracing, no-till farming, cover crops and agroforestry.

Irrigation uses most of the world's freshwater. Flood and furrow irrigation waste water through evaporation and runoff and can cause waterlogging and salinization; drip irrigation is the most efficient. Pumping groundwater faster than it refills depletes aquifers.

Pesticides control pests but can harm nontarget species, accumulate in food chains, and lead to resistance. Integrated pest management combines biological controls, crop rotation, physical barriers and limited chemical use.

The tragedy of the commons describes how individuals acting in their own interest overuse shared resources like fisheries, groundwater and grazing land, depleting them for everyone. Regulations, permits and community management can prevent it.

Forestry practices include clear-cutting (fast and cheap, but causes erosion and habitat loss) and selective cutting. Mining extracts ores and fuels through surface methods like strip mining and mountaintop removal or through subsurface mines, causing habitat destruction, acid mine drainage and tailings; reclamation restores sites. Urbanization brings sprawl, impervious surfaces that increase runoff, and urban heat islands; smart growth and public transit help. Overfishing and bycatch have collapsed fisheries, and aquaculture is growing to meet demand.

Cities reduce runoff and flooding with permeable pavement, green roofs, rain gardens, retention ponds and more vegetation. All of them let more water soak into the ground. That also recharges groundwater, filters pollutants and can cool urban heat islands. Many forests and grasslands are adapted to periodic fire. Prescribed (controlled) burns and clearing underbrush remove built-up fuel, so later wildfires are smaller and less intense.

Overgrazing removes plant cover and compacts soil, which leads to erosion and can cause desertification. Cattle near streams also add sediment, nutrients and bacteria from manure. Rotational grazing, fencing off stream banks (riparian zones) and providing other water sources reduce these impacts. Rotating crops, especially including legumes that host nitrogen-fixing bacteria, restores soil nutrients and reduces the need for fertilizer. It also improves soil structure and breaks the life cycles of pests that specialize on one crop.

Meat requires far more land, water and feed per gram of protein than plant foods, because only about 10% of energy passes up each trophic level. Beef has the largest footprint, partly because cattle digestion releases methane. Concentrated feeding operations also produce manure runoff that pollutes water.

Key ideas

• The Green Revolution boosted yields with fertilizers, pesticides and high-yield crops, but caused pollution.
• Monocultures are efficient but vulnerable to pests.
• Overgrazing, overfishing and overdrafting aquifers are examples of the tragedy of the commons.
• Clear-cutting causes erosion; selective cutting is less damaging.
• Integrated pest management combines methods to reduce pesticide use.

Formulas and rules

Common mistakes

• Thinking flood irrigation is efficient. Drip irrigation wastes far less.
• Forgetting pesticides can lead to resistant pests.

Words to know

Tragedy of the commons

Individuals overuse a shared resource, depleting it for everyone.

Drip irrigation

The most water-efficient irrigation: water goes straight to roots.

Integrated pest management

Combining biological, physical and limited chemical controls.

Monoculture

Growing one crop; one pest or disease can wipe it out.

Clear-cutting

Removing all trees at once; causes erosion and habitat loss.

Sustainable yield

Harvesting no faster than the resource regrows.

Green Revolution

Higher yields from new crop varieties, fertilizer, irrigation and pesticides.

Salinization

Salt buildup in soil from irrigation.

Aquifer depletion

Pumping groundwater faster than it refills.

Pesticide resistance

Pests evolve to survive pesticides.

Selective cutting

Removing only some trees.

Crop rotation

Changing crops each season to protect soil and reduce pests.

No-till farming

Planting without plowing to reduce erosion.

Urban sprawl

Low-density development spreading outward from cities.

Bycatch

Unwanted species caught while fishing.

Aquaculture

Farming fish and other aquatic organisms.

Surface mining

Removing soil and rock to reach ores or coal, as in strip mining.

Mine reclamation

Restoring land after mining.

Sample practice questions

5 more questions like these, from level 1 to 5, are in the practice set.