Free Unit Notes

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I. The Tragedy of the Commons (Topic 5.1)

  A. Shared resources and individual incentives
    1. The tragedy of the commons occurs when people overuse a shared resource because each person gains from taking more while everyone shares the damage.
    2. Examples include overfishing in open-access waters, excessive groundwater pumping, and overgrazing on shared pasture.
    3. Resource use becomes unsustainable when removal exceeds the resource’s ability to recover.

  B. Preventing overuse
    1. Enforced harvest limits, permits, and community agreements can keep use within sustainable levels.
    2. Monitoring and penalties help users follow rules. Ownership alone does not guarantee conservation.

II. Clearcutting (Topic 5.2)

  A. Harvesting trees
    1. Clearcutting removes all or nearly all trees from an area at once. It provides timber efficiently and can lower harvesting costs.
    2. Deforestation is a lasting conversion of forest to another land use. A clearcut that regrows as forest is not necessarily permanent deforestation.

  B. Environmental effects
    1. Removing roots and leaf litter exposes soil to erosion. Increased runoff carries sediment into streams and can increase flooding.
    2. Loss of shade raises soil and stream temperatures. Warmer water holds less dissolved oxygen and can harm cold-water organisms.
    3. Trees store carbon and take in carbon dioxide during photosynthesis. Burning or decomposition releases stored carbon, and tree removal reduces future carbon uptake.
    4. Forest loss reduces pollutant removal and wildlife habitat. Roads and clearings fragment habitat and increase exposure to warmer, drier forest edges.

III. The Green Revolution (Topic 5.3)

  A. Increasing agricultural production
    1. The Green Revolution increased food production through high-yield crop varieties, mechanization, irrigation, fertilizers, and pesticides.
    2. Mechanization allows fewer workers to cultivate larger areas and can increase profits, but often increases fossil-fuel use.
    3. Irrigation supplies water, fertilizers supply nutrients, and pesticides reduce losses to pests.
    4. Genetic engineering directly changes genetic material to produce useful traits. Genetically modified organisms, or GMOs, became widely used after the Green Revolution’s early expansion.
      a. Traditional selective breeding crosses parents with desired traits over generations. A high-yield variety is not necessarily a GMO.

  B. Benefits, costs, and yield
    1. Higher yields increase food supply and may reduce pressure to clear more land. They do not guarantee that land clearing will stop.
    2. Intensive farming can deplete water, pollute waterways, reduce crop genetic diversity, and require costly seeds, machinery, and chemicals.
    3. Crop yield = amount harvested ÷ land area. For example, 120,000 kg harvested from 20 hectares equals 6,000 kg/ha.
    4. Percent increase = [(new value − original value) ÷ original value] × 100. Compare yields using the same units.

IV. Impacts of Agricultural Practices (Topic 5.4)

  A. Soil disturbance and vegetation removal
    1. Tilling turns soil to prepare fields and control weeds. Repeated tilling exposes topsoil to wind and water erosion and speeds organic-matter breakdown.
    2. Heavy machinery can compact soil, reducing spaces for roots, air, and water. Less infiltration can increase runoff.
    3. Slash-and-burn agriculture clears and burns vegetation. Ash briefly adds nutrients, but burning releases air pollutants and carbon dioxide.
    4. Repeated cultivation without enough recovery time depletes soil nutrients and increases erosion. Clearing natural vegetation also removes habitat.

  B. Fertilizers and monoculture
    1. Fertilizers supply nutrients such as nitrogen, phosphorus, and potassium. Both synthetic fertilizer and manure can pollute water when overapplied.
    2. Nutrient runoff can cause eutrophication, in which nutrient enrichment promotes excessive algae growth.
      a. When algae die, decomposers use dissolved oxygen as they break down the dead material. The resulting hypoxia, or low oxygen, can kill aquatic animals.
    3. Leaching carries dissolved substances downward through soil. Nitrate can reach and contaminate groundwater.
    4. Monoculture grows one crop over a large area. It simplifies farming but provides a continuous food supply for pests and can deplete particular nutrients.

V. Irrigation Methods (Topic 5.5)

  A. Supplying water to crops
    1. Irrigation adds water when rainfall does not meet crop needs. Agriculture accounts for about 70% of global freshwater withdrawals.
    2. A withdrawal removes water from its source. Consumptive use is the portion not readily returned for immediate reuse, including water lost through evaporation and transpiration.

  B. Comparing delivery methods
    1. Furrow irrigation sends water through channels between crop rows. It is inexpensive, but roughly one-third of applied water may be lost to runoff and evaporation.
    2. Flood irrigation covers a field with water. It is simple and inexpensive, but can cause waterlogging; an approximate water-loss estimate is 20%.
    3. Spray irrigation pumps water through overhead nozzles. It covers large areas but requires energy and equipment; about one-quarter or less may be lost.
    4. Drip irrigation slowly releases water near roots. Approximate losses are only 5%, but installation is costly and emitters can clog.
    5. These loss values are approximate. Weather, soil, and system management affect actual efficiency, so the methods do not have one universal ranking.

  C. Soil damage and groundwater depletion
    1. Waterlogging fills soil pores with water, limiting the oxygen available to roots for cellular respiration.
    2. Salinization is salt buildup in soil as irrigation water evaporates or is taken up by plants. High salt levels make water uptake harder and can damage crops.
    3. Drainage and carefully managed flushing can reduce salt buildup, but flushing requires more water and produces salty drainage.
    4. An aquifer stores and transmits groundwater. Pumping faster than recharge lowers groundwater levels, as in depleted parts of the Ogallala Aquifer.
    5. Efficient irrigation and crops suited to local rainfall reduce demand. Expanding irrigated acreage can cancel these savings.

  D. Water-use calculations
    1. Irrigation efficiency = useful water delivered ÷ water applied × 100. Use matching volume units.
    2. Water required = crop water need ÷ efficiency as a decimal. Delivering 950 L at 95% efficiency requires 1,000 L of applied water.

VI. Pest Control Methods (Topic 5.6)

  A. Chemical and genetic controls
    1. A pesticide controls an organism that harms crops or other human interests. Insecticides target insects, herbicides target weeds, fungicides target fungi, and rodenticides target rodents.
    2. Pest control protects yields, but pesticides can harm workers, pollinators, natural predators, and other non-target organisms. Drift and runoff spread exposure.
    3. Some engineered crops resist pests or diseases. Others tolerate herbicides, allowing weeds to be treated without killing the crop.
    4. Reliance on a few crop varieties can reduce genetic diversity. Genetic engineering does not itself require all farms to plant the same variety.

  B. Resistance and persistent chemicals
    1. Pesticide resistance evolves when pests with inherited survival traits reproduce after treatment. Repeated use increases resistant individuals in the population.
    2. Pesticide use creates selection pressure; individual pests do not develop inherited resistance because they need it.
    3. The pesticide treadmill occurs when resistance or loss of natural predators leads to repeated or heavier pesticide use.
    4. Rotating modes of action and combining controls can slow resistance. Non-Bt refuge crops help preserve susceptible insects near crops producing insect-killing Bt proteins.
    5. Bioaccumulation is buildup of a chemical within an organism over time. Biomagnification is increasing concentration at higher feeding levels.
      a. Persistent, fat-soluble pesticides may show both processes. Not all pesticides persist or biomagnify.

VII. Meat Production Methods (Topic 5.7)

  A. Concentrated and pasture-based systems
    1. Concentrated animal feeding operations (CAFOs) confine many animals and provide feed, often grain and soy. High output can lower production costs and consumer prices.
    2. Concentrated manure can contaminate waterways with nutrients and pathogens. Decomposition can release methane and ammonia.
    3. Antibiotic use can select for resistant bacteria. The bacteria become resistant, not the people exposed to them.
    4. Pasture-based systems let animals eat grass or forage for much of their lives. Manure returns nutrients to soil, but high animal density still causes runoff and erosion.
    5. Pasture systems often require more land and cost more. Free-range animals are not necessarily raised without antibiotics.

  B. Overgrazing and resource demand
    1. Overgrazing occurs when animals remove vegetation faster than it regrows. Trampling compacts soil, while loss of plant cover increases erosion.
    2. Overgrazing reduces fertility, biodiversity, and carbon storage. In dry regions it can cause desertification, the loss of productive land.
    3. Rotational grazing moves animals between pastures so plants can recover. Herd size and recovery time must match local conditions.
    4. Meat production generally requires more land, water, and energy per gram of protein than plant-food production because animals use much of their feed energy for metabolism.
    5. Ruminants such as cattle and sheep release methane from digestion. Feed production, fertilizer, transport, and manure also contribute greenhouse gases.
    6. Eating less meat, especially ruminant meat, can reduce resource demand and emissions. Better feed, precise nutrient use, manure management, and land restoration can also reduce impacts.

VIII. Impacts of Overfishing (Topic 5.8)

  A. Population and ecosystem effects
    1. Overfishing removes fish faster than populations can replace them. Efficient gear, high demand, and open access can increase harvest pressure.
    2. Removing breeding adults slows recovery. Depleted populations disrupt food webs and threaten food supplies and fishing jobs.
    3. Bycatch is the unintended capture of non-target animals. Nets and longlines can catch turtles, seabirds, and other wildlife.
    4. Bottom trawling drags fishing gear across the seafloor and damages bottom habitats.

  B. Reducing harvest pressure
    1. Enforced catch limits, seasonal closures, protected areas, and size limits can help populations recover.
    2. More selective gear and turtle-excluder devices reduce bycatch. Monitoring helps managers adjust limits as populations change.
    3. Catch per unit effort = catch ÷ fishing effort, such as kilograms per boat-day. Falling values may indicate depletion even when total catch stays stable.

IX. Impacts of Mining (Topic 5.9)

  A. Extraction methods and wastes
    1. An ore contains enough valuable material to make extraction economically worthwhile. Lower-grade deposits require more rock processing for the same product.
    2. Surface mining removes overlying soil and rock, called overburden, to reach shallow deposits. Methods include strip mining, open-pit mining, and mountaintop removal.
    3. Subsurface mining uses shafts and tunnels to reach deeper deposits. It can disturb less surface land but creates collapse, dust, gas, and worker-safety hazards.
    4. Mining removes habitat, increases erosion and dust, and uses energy and water. Underground excavations can cause subsidence, or sinking ground.
    5. Tailings are residues from ore processing. Slag is waste from smelting. These differ from overburden removed before extraction.

  B. Pollution and restoration
    1. Acid mine drainage forms when exposed sulfide minerals react with oxygen and water, producing acid that can mobilize toxic metals.
    2. Acidic drainage can harm aquatic life and persist after closure. Its occurrence depends on the minerals and site conditions.
    3. Reclamation reshapes disturbed land, replaces topsoil, restores vegetation, and manages polluted drainage. It may not recreate the original ecosystem.
    4. Mining supplies useful materials and jobs. Reusing and recycling metals reduce demand for extraction and the waste it produces.
    5. Ore mass required = desired metal mass ÷ ore grade as a decimal, assuming complete recovery. At 2% grade, 100 kg of ore contains 2 kg of metal.

X. Impacts of Urbanization (Topic 5.10)

  A. Development and water movement
    1. Urbanization increases urban development and the share of people living in cities. Construction uses resources and removes or fragments habitat.
    2. Impervious surfaces, such as roads and roofs, prevent infiltration. Runoff reaches streams quickly, increasing peak flow, flooding, erosion, and pollutant delivery.
    3. Reduced infiltration lowers groundwater recharge. Storm drains may carry polluted runoff directly to waterways without treatment.
    4. Excessive coastal groundwater pumping can cause saltwater intrusion: lowered freshwater pressure allows seawater to enter aquifers and wells.

  B. Sprawl, energy, and heat
    1. Urban sprawl spreads low-density development into rural areas. Greater distances between homes and destinations increase driving and land use.
    2. Fossil-fuel use releases carbon dioxide, vegetation removal reduces carbon storage, and landfill decomposition produces methane.
    3. The urban heat island effect makes cities warmer than nearby rural areas because surfaces absorb heat and vegetation provides less evaporative cooling.
    4. Compact development, public transit, and reuse of developed land can reduce driving and land demand per person.

XI. Ecological Footprints (Topic 5.11)

  A. Measuring environmental demand
    1. An ecological footprint estimates the biologically productive land and water needed to supply resource use and absorb associated wastes, especially carbon dioxide.
    2. Diet, transportation, housing, energy, purchases, and waste influence footprint size. A carbon footprint measures greenhouse gas emissions rather than productive area.
    3. Footprints are often expressed in global hectares (gha), which account for average biological productivity.
    4. Biocapacity is ecosystems’ ability to regenerate resources and absorb relevant wastes. Demand above available biocapacity creates an ecological deficit; global excess is ecological overshoot.

  B. Interpreting comparisons
    1. Distinguish total footprint from footprint per person. Total footprint = population × average footprint per person.
    2. A larger population can have greater total demand despite a lower footprint per person. Footprints do not measure every effect on biodiversity or water quality.

XII. Introduction to Sustainability (Topic 5.12)

  A. Resource use over time
    1. Sustainability meets present needs while maintaining resources and environmental conditions for future generations.
    2. Renewable resources can be depleted when use exceeds recovery. Nonrenewable resources do not regenerate on a human time scale; conservation, reuse, and recycling extend supplies.
    3. Sustainable yield is the harvest that maintains a renewable resource’s long-term supply. It depends on resource growth, ecosystem needs, and changing conditions.
    4. Ending stock = starting stock + net addition before harvest − harvest. A harvest above net addition reduces stock if other conditions stay unchanged.

  B. Evaluating environmental conditions
    1. Sustainability indicators include biodiversity, food production, human population, resource depletion, atmospheric carbon dioxide, and average global surface temperature.
    2. Compare several indicators over time. Increasing food output alone does not show sustainability if soil fertility or groundwater supplies are declining.

XIII. Methods to Reduce Urban Runoff (Topic 5.13)

  A. Increasing infiltration and slowing flow
    1. Permeable pavement allows water into an underlying layer and, where conditions permit, into soil. This reduces surface runoff and can improve recharge.
    2. Trees intercept rainfall and take up water. Rain gardens and bioswales, or vegetated channels, slow runoff and help trap sediment and pollutants.
    3. Green roofs retain rainfall in vegetation and growing material. Rain barrels and cisterns store roof runoff for later use.
    4. Retention ponds hold water, while detention basins temporarily store runoff and release it slowly. Not every basin recharges groundwater.
    5. Public transit and building upward reduce road and parking area per person. Protecting wetlands and streamside vegetation also slows and stores water.

  B. Evaluating runoff solutions
    1. Infiltration systems need suitable soils, groundwater depth, and maintenance. They should not direct contaminated runoff into drinking-water aquifers.
    2. A storm hydrograph shows stream discharge over time. Impervious land typically produces an earlier, higher peak; infiltration and storage delay and reduce it.
    3. Compare pavement treatments using equal areas, slopes, rainfall, soil, and starting moisture. Change pavement type and measure runoff volume; include ordinary pavement and replicate plots.
    4. Runoff volume = rainfall depth × area × runoff fraction. Using depth in meters and area in square meters gives volume in cubic meters; 1 m³ = 1,000 L.

XIV. Integrated Pest Management (Topic 5.14)

  A. Combining control methods
    1. Integrated pest management (IPM) uses prevention, monitoring, and multiple controls to limit pest damage while minimizing environmental harm.
    2. Identify pests, monitor abundance, act at an action threshold where damage justifies treatment, and evaluate the results.
    3. Cultural controls include crop rotation, intercropping, resistant varieties, and removal of infected plants. Intercropping grows different crops together.
    4. Physical controls include traps, screens, barriers, and mechanical weed removal. Biological controls use predators, parasites, or other natural enemies.
    5. Targeted pesticides may be used when necessary. IPM does not require eliminating all pests or avoiding every chemical treatment.

  B. Benefits and limitations
    1. IPM can reduce pesticide exposure, water pollution, harm to wildlife, and selection for resistance while maintaining yields.
    2. It can require more knowledge, labor, monitoring, and initial expense. Introduced biological controls can harm non-target species or become invasive.
    3. Compare pesticide use, yield, costs, and non-target effects under similar conditions. Reduced chemical use is most useful when acceptable pest control is maintained.

XV. Sustainable Agriculture (Topic 5.15)

  A. Conserving soil
    1. Contour plowing follows equal elevations across a slope, slowing runoff. Terracing creates flatter hillside steps that shorten slopes and reduce erosion.
    2. No-till agriculture plants with little soil disturbance and leaves protective residues. It reduces erosion, although weeds still require control.
    3. Strip cropping alternates crop strips to trap sediment and interrupt runoff. Windbreaks use trees or shrubs to slow wind and reduce wind erosion.
    4. Perennial crops live for several years, keeping roots and cover in place. Cover crops protect otherwise bare soil between cash crops.

  B. Maintaining fertility and other resources
    1. Crop rotation changes crops between seasons, helping manage nutrient demand and disrupt pest cycles.
    2. Legumes support nitrogen-fixing bacteria in root nodules. These bacteria convert atmospheric nitrogen into biologically usable forms; decomposing residues can supply later crops.
    3. Green manure consists of plants grown and returned to soil. Compost and animal manure also add nutrients and organic matter, but overapplication can pollute water.
    4. Agricultural limestone raises the pH of overly acidic soil, improving conditions for growth. Apply it according to soil tests; it does not replace nitrogen fertilizer.
    5. Rotational grazing allows pasture recovery. Efficient irrigation, suitable crops, mulching, and IPM can further conserve water and soil.
    6. Match each practice to the problem and local conditions. Costs, labor, climate, and crop markets affect whether a method is practical.

XVI. Aquaculture (Topic 5.16)

  A. Producing aquatic food
    1. Aquaculture raises aquatic organisms under managed conditions, such as fish in ponds, shrimp in coastal ponds, or oysters on racks. Mariculture is aquaculture in marine water.
    2. Aquaculture can provide high food output from a small area and predictable harvests. Some systems need less fuel than fishing vessels.
    3. Feed and energy needs vary. Carnivorous fish may require feed from wild fisheries, while shellfish usually filter naturally available food.

  B. Environmental effects and management
    1. Uneaten feed and waste add nutrients and organic matter, causing eutrophication and oxygen depletion. Treatments may also affect nearby organisms.
    2. Dense populations spread disease and parasites, which can reach wild fish. Escaped organisms can compete or interbreed with wild populations.
    3. Some coastal shrimp ponds replace mangrove habitat. Aquaculture therefore does not automatically protect ecosystems or remove pressure on wild fisheries.
    4. Careful siting, escape barriers, lower stocking densities, disease prevention, and waste treatment reduce harm. Recirculating systems reuse water but require energy and equipment.

XVII. Sustainable Forestry (Topic 5.17)

  A. Maintaining forest resources
    1. Sustainable forestry maintains wood supplies while protecting biodiversity, soil, water, and carbon storage.
    2. Selective cutting removes chosen trees while retaining much of the canopy. Careful roads and harvesting methods limit damage to soil and remaining trees.
    3. Longer harvest rotations, mixed-age stands, wildlife corridors, and uncut streamside buffers protect forest functions.
    4. Reforestation restores trees on previously forested land. Suitable native species and species mixtures can improve habitat and resilience.
    5. Buying sustainably harvested wood, reusing lumber, and recycling paper reduce pressure for new logging. New plantations do not immediately replace mature-forest habitat.

  B. Managing pests and fire
    1. IPM and targeted removal of infected trees can reduce insect and pathogen damage. Avoid unnecessary disturbance to healthy habitat.
    2. A prescribed burn is a planned fire under controlled conditions. In fire-adapted forests, it reduces accumulated fuel and can lower the severity of later wildfires.
    3. Prescribed burns require suitable weather and safeguards against smoke and escaped fire. They do not prevent all wildfires and are not appropriate for every ecosystem.

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