Unit 5: Land and Water Use

Tragedy of the Commons

  • Definition: A common resource available for all humans, often exploited unsustainably for profit.
  • Examples:
    • Ocean (overfishing, dead zones from fertilizer runoff)
    • Atmosphere
    • Public rangelands (overgrazing)
  • Problem: Resources are depleted because individuals prioritize personal profit over sustainability.
  • Ocean Example:
    • Overfishing: Nets damage fish populations and the ocean floor.
    • Dead Zones: Fertilizer runoff (e.g., Mississippi River into Gulf of Mexico) leads to oxygen depletion.
  • Groundwater Depletion:
    • Often unregulated and overdrafted (more water taken out than replenished).

Water Resources

  • Ogallala Aquifer:
    • Location: Central U.S. (Texas to Midwest).
    • Largest aquifer in the U.S., one of the biggest in the world.
    • Problem: Largely overdrafted and nearing depletion.
  • Limited Freshwater Availability:
    • Only a small percentage of Earth's water is accessible freshwater.
    • Importance of careful usage to avoid pollution, misuse, and depletion.
  • Aquifers (Groundwater):
    • Confined: Under pressure.
    • Unconfined: At air pressure.
    • Overdrafting: Aquifers not recharging quickly enough.
  • Subsidence:
    • Definition: Sinking of land level due to water removal from aquifers.
    • Process: As water is drawn out, the land above can sink.
  • Saltwater Intrusion:
    • Occurs: Aquifers near coastlines.
    • Process: Over-extraction of freshwater allows saltwater to intrude, contaminating the aquifer.

Water Usage: Irrigation

  • Irrigation Usage: ~70% of freshwater used globally is for agriculture and lawn irrigation.
  • Types of Irrigation:
    • Furrow Irrigation:
      • Description: Water flows through rows between plants.
      • Evaporation: High (~40%).
    • Flood Irrigation:
      • Description: Flooding the entire field.
      • Evaporation: High, similar to furrow.
    • Spray Irrigation:
      • Description: Sprinklers spray water over crops.
    • Drip Irrigation:
      • Description: Water drips slowly through punctured lines.
      • Evaporation: Least evaporation; avoids salinization.
  • Salinization:
    • Definition: Accumulation of salts in the soil due to evaporation of irrigation water.
    • Fix: Flushing (applying more water), but this can also deposit more minerals.

Agricultural Impacts

  • Tillage:
    • Definition: Turning over soil to aerate it.
    • Problem: Erosion, loss of topsoil.
    • Topsoil: Important for nutrients and water retention.
  • Erosion:
    • Definition: Washing away of soil.
    • Solution: Cover crops (plants between main crops) to hold soil with roots.
  • Desertification:
    • Definition: Soil loses nutrients and can no longer support plant life.
    • Causes: Overgrazing on rangelands, general soil degradation.
  • Overgrazing:
    • Impacts: Grass constantly removed, nutrient loss, erosion.
  • Salinization:
    • Appearance: White crust on the soil surface.
    • Cause: Irrigation water evaporates, leaving salts and minerals.
    • Impact: Prevents plant growth due to osmotic potential (plants can't absorb enough water).
  • Integrated Pest Management (IPM):
    • Definition: Reducing pesticide use through various methods.
    • Methods:
      • Crop Rotation: Changing crops to disrupt pest cycles.
      • Natural Predators: Using beneficial insects (e.g., ladybugs eating aphids).
      • GMOs: Genetically modified organisms resistant to pests.
      • Mulch: Prevents weed growth.

Mining

  • Ore: Rock containing a profitable amount of minerals.
  • Reserves: Known sources available for mining.
  • Depletion Time: When ~80% of reserves are used up.
  • Overburden: Soil removed during mining.
  • Spoils: Waste created by mining processes.
  • Tailings: Mining residue from water usage during mining.
  • Impacts:
    • Disruption of Land and Habitat: Removal of plants, trees, and topsoil.
    • Spoils Banks: Covering good topsoil.
    • Liquids/Tailings: Can contain toxic chemicals (e.g., Samarco Dam collapse in Brazil).
    • Water Quality Impacts: Erosion leads to sediments in waterways, blocking sunlight and harming aquatic life.
  • Erosion:
    • Definition: Soil moved by wind or water.
    • Impact: Loss of fertile topsoil.

Fishing Impacts

  • Bycatch:
    • Definition: Unintentional catch of non-target organisms.
    • Examples: Juvenile fish, dolphins, turtles.
    • Impact: Often killed in nets.
  • Fishery Collapse:
    • Definition: Decline in fish population by >90% in a region.
    • Impact: Difficult for populations to recover due to limited size and genetic bottleneck.
  • Other Impacts:
    • Ocean Pollution: Fishing equipment dumped intentionally or unintentionally.
    • Damage to Seafloor/Coral Reefs: Nets with weights tear up delicate ecosystems.
  • Solutions:
    • Laws and Regulations: Limiting catch, seasonal restrictions.
    • Community-Based Management: Local communities manage resources.
    • Marine Reserves: Protected areas.
    • Monitoring: Tracking fish populations.
    • Consumer Choice: Avoiding over-harvested fish.
    • Reducing Government Subsidies: Removing financial support that encourages overfishing.
  • Aquaculture:
    • Definition: Growing fish in tanks or netted areas.
    • Pros: Cost-effective, less land needed.
    • Cons:
      • Waste Contamination: High density leads to concentrated waste.
      • Disease: Spreads quickly in close quarters.
      • Escaped Fish: Can outcompete wild fish.
      • Antibiotic Use: To keep fish healthy.

Forests and Deforestation

  • Benefits of Forests:
    • Soil Stabilization: Roots prevent erosion.
    • Slow Runoff: Water infiltrates into the ground, lessening flooding.
    • Water Purification: Percolation into groundwater.
    • Carbon Sinks: Absorb carbon dioxide during photosynthesis.
  • Drawbacks of Deforestation:
    • Altered Landscapes and Habitats.
    • Soil Degradation: Loss of topsoil, erosion.
    • Increased Carbon in Atmosphere.
    • Increased Runoff: Carrying sediments into waterways.
  • Fire Suppression:
    • Problem: Woody accumulation leads to larger, uncontrollable fires.
    • Solution: Controlled or prescribed burning to prevent buildup.
  • Clear Cutting:
    • Definition: Cutting down every tree in an area.
    • Impact: Destroys forest communities, causes soil erosion.
  • Selective Cutting:
    • Definition: Cutting down only certain trees, leaving others to maintain the forest.
  • Rangeland
    • Overgrazing:
      • Eating away at grass and eventually damaging the soil.
    • Erosion:
      • Lack of plants like grass holding the soil in place.
    • Cattle waste and waterways within the rangeland.
      • Eutrophication
      • Trampling the edges of stream beds causing further erosion.
    • Solutions to prevent overgrazing:
      • Fence streams or protect in some way.
      • Supplement the cows feed.
      • Moving the cattle from range area to range area.

Urbanization

  • Impervious Surfaces:
    • Definition: Surfaces that don't allow water to seep through (e.g., concrete, asphalt, rooftops).
    • Impact: Increased runoff into sewer drains and waterways.
  • Runoff Problems:
    • Increased velocity and volume of streams.
    • Habitat damage, erosion, flooding.
    • Pollution: Car oil, pesticides, fertilizers, animal feces into waterways.
  • Eutrophication:
    • Nutrients (nitrogen and phosphorus) cause algae overgrowth.
    • Algae die and decay, consuming oxygen.
    • Hypoxia/dead zones form.

Meat Production

  • Concentrated Animal Feeding Operations (CAFOs):
    • Definition: High-density growth of animals (cows, pigs, chickens) for food.
    • Pros: Efficient, minimizes land use.
    • Cons:
      • Antibiotic Resistance: Due to widespread antibiotic use to combat disease.
      • Concentrated Waste: Leads to eutrophication.
      • Ethical Issues: Densely packed animals in confined spaces.