📚Study Guide: Land and Water Use
Unit 5: Land and Water Use
Human use of land and water resources shapes the surface of the planet and determines the sustainability of civilization. This unit covers agriculture, forestry, mining, urbanization, and water management. Students must understand the Green Revolution--the mid-20th century introduction of high-yield crop varieties, irrigation, and synthetic fertilizers/pesticides that dramatically increased food production but also caused environmental degradation. Modern agricultural practices include monocropping, concentrated animal feeding operations (CAFOs), and the use of genetically modified organisms (GMOs). Each has distinct environmental impacts: soil erosion, nutrient runoff, water depletion, and biodiversity loss. Irrigation methods vary in efficiency: flood irrigation is cheap but wastes water; drip irrigation is highly efficient but expensive. Forestry practices range from clear-cutting (maximizes short-term yield but destroys habitat) to selective cutting and sustainable certification (FSC). Mining techniques include surface (strip, open-pit, mountaintop removal) and subsurface methods, each with distinct impacts on land, water, and air quality. Urbanization replaces permeable surfaces with impervious ones, increasing runoff, flooding, and the urban heat island effect. Water use categories include agricultural (70% globally), industrial (20%), and domestic (10%). The AP exam frequently asks students to evaluate trade-offs between resource extraction and environmental protection, calculate water footprints, and propose sustainable management strategies.
Key Concepts
- Agricultural Practices: Monocropping increases efficiency but reduces genetic diversity and increases pest vulnerability. CAFOs produce large quantities of meat but generate massive waste and antibiotic resistance. GMOs can reduce pesticide use and increase yields but raise ecological and ethical concerns.
- Soil Conservation: Techniques include contour plowing, terracing, no-till agriculture, crop rotation, cover crops, and windbreaks. These reduce erosion, maintain soil structure, and preserve organic matter.
- Irrigation Methods: Flood (inexpensive, 50% efficient), furrow (60-70% efficient), spray/sprinkler (75-85% efficient), drip (90-95% efficient, most expensive). Salinization occurs when irrigation water evaporates, leaving salts behind.
- Forestry: Clear-cutting removes all trees; selective cutting removes individual trees. Sustainable forestry balances timber production with ecosystem health. Old-growth forests store large amounts of carbon and harbor high biodiversity.
- Mining Impacts: Acid mine drainage (sulfide minerals oxidize to produce sulfuric acid), tailings disposal, habitat destruction, and subsidence. Reclamation attempts to restore mined land but often fails to replicate original ecosystems.
- Urbanization: Paved surfaces increase stormwater runoff, decrease groundwater recharge, and elevate temperatures (urban heat island). Green infrastructure (green roofs, permeable pavement, rain gardens) mitigates these effects.
Vocabulary
- Green Revolution: The development and introduction of high-yield crop varieties, expanded use of irrigation, synthetic fertilizers, and pesticides beginning in the 1940s-1960s.
- CAFO (Concentrated Animal Feeding Operation): A large-scale animal agriculture facility where animals are confined and fed; produces high output but concentrated waste.
- Salinization: The accumulation of salts in soil due to evaporation of irrigation water, reducing soil fertility and crop yields.
- Overburden: The soil and rock removed to access ore deposits in surface mining.
- Watershed: The land area that drains into a particular body of water; critical unit for managing water quality and quantity.
- Urban Heat Island: The phenomenon where urban areas are significantly warmer than surrounding rural areas due to heat-absorbing surfaces and reduced evapotranspiration.
Essential Formulas
- Water Use Efficiency = (crop yield / water applied)
- Soil Loss Equation (simplified): A = R x K x LS x C x P (R = rainfall, K = soil erodibility, LS = slope, C = cover, P = practice)
Common Mistakes
- Confusing Pest Resistance and Pesticide Resistance: Pest resistance is a plant's natural ability to resist pests. Pesticide resistance is when pests evolve to survive chemical applications.
- Thinking All GMOs Are Harmful: Evaluate GMOs based on evidence: some reduce pesticide use (Bt crops) and increase nutritional value (Golden Rice), while others raise concerns about gene flow and corporate control.
- Confusing Salinization and Waterlogging: Salinization is salt accumulation. Waterlogging is saturated soil due to over-irrigation, which prevents root aeration.
- Underestimating Urban Impacts: Urbanization affects not just land cover but also local climate, hydrology, air quality, and biodiversity.
AP Exam Strategies
- Compare Agricultural Methods: When asked to evaluate farming practices, use a trade-off framework: yield vs. water use vs. pollution vs. biodiversity.
- Calculate Water Efficiency: Be able to compare irrigation methods using efficiency percentages and explain why drip irrigation reduces both water waste and salinization risk.
- Propose Sustainable Solutions: For any resource problem, propose integrated strategies (e.g., contour plowing + cover crops + buffer strips for soil conservation).
- Link Land Use to Water Quality: Explain how deforestation, agriculture, and urbanization increase sediment, nutrient, and pollutant loads in waterways.
Real-World Applications
- Dust Bowl: Poor soil management (deep plowing, removal of native grasses) combined with drought caused catastrophic erosion in the 1930s US Great Plains, demonstrating the importance of conservation practices.
- Aral Sea Collapse: Diversion of rivers for Soviet cotton irrigation shrank the Aral Sea by 90%, creating a dustbowl of toxic sediments and destroying a fishing industry.
- Singapore's Water Management: A combination of rainwater harvesting, advanced wastewater recycling (NEWater), and desalination allows the city-state to be nearly water-independent despite having no natural aquifers.