Introduction to Environmental Science - Water Usage and Quality

Introduction to Environmental Science (GEOL 125)

• Welcome to the course!
• Signup sheets are available for article discussions at 8:30 and 11:30.
• Weekly modules provide access to the textbook and assignments.
• A Zoom link will be provided if virtual meetings are scheduled.
• Syllabus is pending.
• Contact Priya Ganguli at priya.ganguli@csun.edu.
• Signup sheet available for finding a discussion partner.

Chapter 7: Water - Usage and Quality

• Focus: How we use water and how our actions affect its quality.

Importance of Water

• Why do we care about water?
• What is water?

Water Uses

• What do we need water for?
• Public Supply: Drinking, showering, cooking, home irrigation, commercial uses.
  • Accounts for approximately 12% of U.S. water use.
  • Note: Data is from an older report (2015) as the most recent USGS report is not yet available.
• Irrigation: Crucial for crops.
  • Consumes a significant portion of water: approximately 32%.
  • Note: Data is from an older report (2015) as the most recent USGS report is not yet available.
• Electric Power Generation: The largest use of water.
  • Accounts for approximately 46% of water use.
  • Water is converted to steam to turn turbines (using fossil fuels, nuclear energy, etc.).
  • Water is sometimes recycled, sometimes not.
  • Note: Data is from an older report (2015) as the most recent USGS report is not yet available.
• Other smaller uses:
  • Mining
  • Livestock
  • Aquaculture (fish farms)

Embedded Water

• Hidden water usage within products.
• Examples:
  • Over 500 gallons for 1 pound of pork.
  • Over 100 gallons for 1 pound of potatoes.
  • 700 gallons for 1 gallon of beer.
  • Over 400 gallons for 1 chocolate bar.

Changes in U.S. Water Use Over Time

• Total water use (dark blue line) and U.S. population (red line) trends:
  • Water use increased significantly from 1950 to 1980.
  • Leveled off in the 1980s.
  • Declined in the 2000s despite continued population growth. Why?

Factors Influencing Water Use Changes

• Increased efficiency:
  • 9% reduction in irrigation due to improved methods (flood irrigation to sprinklers to drip irrigation).
  • Some public supply decreases, but not universally.
  • 20% reduction in power generation due to increased use of recirculated water.
  • Fracking contributing to efficiency with newer natural gas plants.

State Water Usage

• States using the most water:
  • California: 9%
  • Texas: 7%
  • Idaho: 6%
  • Arkansas: 4%
  • Florida: 5%
• California: High irrigation (Central Valley), power generation, and population.
• Texas: Significant power generation and overall high demand.
• Idaho & Arkansas: High irrigation and aquaculture despite smaller populations.
• Florida: Population, power generation, and irrigation demands.
• Illinois: Significant coal power and public water supply needs.

Global Water Availability

• Issue: Most of Earth's water is saltwater.
• Why is this a problem?

Salinity Levels

• Water Type and Salinity (parts per million - ppm):
  • Freshwater: < 1,000 ppm
  • Slightly saline: 1,000 – 3,000 ppm
  • Moderately saline (brackish): 3,000 – 10,000 ppm
  • Highly saline: 10,000 – 35,000 ppm
  • Hyper saline: > 35,000 ppm
• Why is saltwater a problem?
  • Cannot be directly used for drinking, irrigation, or power generation.

Freshwater Distribution

• Only 2.8% of Earth’s water is freshwater.
  • Equivalent to 10^{19} gallons.
• Accessibility issues:
  • 70% of freshwater is locked in ice (polar ice caps).
  • 30% is groundwater (variable accessibility).
  • Only ~0.25% is surface water (lakes + rivers).
  • Other factors: distance from cities, contamination.

Water Reservoirs and Residence Time

• Reservoirs: Parts of Earth where water remains for a period (natural or artificial).
• Hydrosphere: Composed of Earth's water reservoirs.
• Residence time: Average time a water molecule spends in a particular reservoir.

Earth's Spheres

• Lithosphere
• Biosphere
• Cryosphere
• Hydrosphere
• Atmosphere

Residence Time Ranking

• Ranked residence time in various reservoirs:
  • Oceans
  • Rivers
  • Atmosphere
  • Groundwater

Actual Residence Times

• Atmosphere: 9 days
• Rivers: 17 days
• Groundwater: 330 years
• Oceans: 2,900 years

Precipitation and Aquifers

• 75% of global precipitation falls into oceans.
• Aquifers: Subsurface areas of rocks or sediments where water accumulates.
• Water slowly passes through aquifers into oceans, lakes, and rivers at a rate of 1 foot per year.

The Water Cycle

• Water cycle: Shifts molecules of water into different places or states of matter around Earth.
• Major water reservoirs and average residence time:
  • Atmosphere: 10 days (0.001% of Earth's water)
  • Soil: 1-2 months (0.001% absorbed by soil)
  • Living Organisms: hours to days (0.0001% consumed by living things)
  • Freshwater Bodies:
    • Lakes: 10 years (0.007%)
    • Rivers/streams: 2-6 months (0.0002%)
  • Ice, Glaciers, Snow and Permafrost:
    • Ice caps: 200,000 years
    • Flowing glaciers: 100 years
    • Winter snow: 2-6 months
    • Permafrost: 50 years (water frozen for > 2 years)
  • Ocean: 3,000 years (96.5% of Earth's water)
  • Groundwater: 100-10,000 years (0.76% of Earth's water)

Key Processes in the Water Cycle

• Evaporation: Water turns into vapor and enters the atmosphere (from ocean and land).
• Evapotranspiration: Plants contribute to evaporation.
• Precipitation: Water returns to Earth in various forms (rain, snow, sleet, hail, freezing rain).
• Surface Runoff: Water from rain or melting snow/ice flows into rivers, lakes/ponds, or the ocean.
• Infiltration: Water seeps into the subsurface, becoming soil moisture or groundwater.

Precipitation Forms

• Rain
• Snow
• Sleet
• Hail
• Freezing Rain
• Fog
• Volcanic eruptions: Introduce water vapor into the atmosphere.

Reservoirs

• We can think of compartments as reservoirs
• A water molecule moves from one part of the environment to another

Surface Water Sources

• Directly from natural lakes.
• From rivers: Example: Drinking water intake for Minneapolis on the Mississippi River.

Human-Made Reservoirs

• Reservoirs behind dams: Approximately 350 dams built in the U.S. around 1900-1950.
• Advantages over rivers:
  • Store extra water during wet years for use during dry years.
  • Hydroelectric power generation.

Downsides to Dams

• Sediment buildup behind the dam, leading to loss of capacity.
• Scouring downstream, causing loss of fish habitat and beach erosion.
• Impeding salmon migration upstream.
• Destruction of terrestrial habitat.