freshwater resources

Week 7: Freshwater Resources

Hydrologic Cycles

  • water covers _% of the Earth’s surface

  • reservoir - a body of water in the hydrologic cycle

  • flux - movement of water among reservoirs

  • water constantly recycles; volume does not change → renewable resource

Water residence

  • some recirculates within days, some residence time measured in 1000s of years

Distribution

  • ~3% of the world’s water = freshwater:

    • ~2% of the world’s water = frozen

    • <1% of the world’s water = accessible to humans (mostly groundwater)

    • Availability

Arid Regions

  • 1/3 of the Earth’s surface with 1/5 of the population ← these regions have water supply problems

World Water Supply

  • water use in the developed world is high

  • humans need a minimum of 50L of water per day

  • flushing toilets is the single largest use of domestic water: ~25%

  • daily water use per state

  • societies use half of all accessible runoff, mostly for irrigation

  • heavy consumption by agriculture (70%), power plants, and manufacturing

  • virtual water - total amount of embedded water, also called water footprint

  • higher on food chain or the more processed = greater virtual water

  • chart

  • cattle products use the most water

  • eating one 6oz red meat patty:

    • ~700 gal of water

    • ~23 bathtubs

    • ~41 showers

  • ditching meat reduces your water footprint by ~60%

Environmental Impacts

  • irrigation is 70% of the water humans use

    • soil pollution (salinization)

    • water pollution & waste

    • fertility loss

  • California Central Valley Project and State Water Project - demands not met because of uneven distribution, overuse, pollution

  • the Colorado River - America’s most arid basin supports agriculture and industry (over-appropriated)

  • subsurface water contained in pore spaces in unconsolidated rocky material and bedrock:

    • unsaturated zone: mix of air & water

    • saturated zone: saturated with water

    • water table: top of saturated zone

  • groundwater overdraft - pumping groundwater faster than recharge → land subsidence

Bad habits or lack of knowledge

  • 3 gal virtual water to make 1 gal bottled water

  • plastic bottles: questionable quality, made of petroleum, sent to landfills, pollution when incinerated, harmful to marine wildlife

Effects of Climate Change

  • greater flooding; increased drought

  • glaciers shrinking → meltwater source disappearing

Sustainable Tactics

  • largest domestic water use in US: toilet

    • residential: 5.1 flushes per person per day

    • work placE: 3 flushes per person per day

  • from 3.0-7.0 gpf to ~1.6 gpf (gallons per flush)

    • dual-flush toilet: ~1.6 gpf solid waste; ~0.8 gpf liquid waste

    • urinal: ~1.0 gpf maximum

  • 2nd largest domestic use: Shower heads & faucets

    • from 3.0-8.0 to 2.2-2.5 gpm (gal/min)

  • 3rd largest domestic use: cloth waters

    • 0.37 load per person per day

    • from 35 to 27 gpl (gal/load)

  • rainwater harvesting

Graywater & Blackwater

Graywater:

  • Bathroom & Laundry

  • toilets, irrigation, cooling-tower makeup water, fire suppression systems

Blackwater:

  • Toilet & Kitchen

  • black pipes not mixed with gray water

  • purified through biological method

  • used for irrigation or released in rivers

Landscaping

  • CA: 40-60% of residential water to grass

  • reduction through:

    • xeriscaping: use native or regionally adapted plants; avoid lawns

    • use mulch, leaves to retain moisture

    • use drip irrigation

  • Bad Habits: Diet

Water Efficiency Program

  • new york city has a massive water supply system

  • in the 1970s, water needs exceeded system capacity in NYC

    • conservation was required to reduce demand

    • public education

    • rebated for high-efficiency toilets, water meter installation, leak detection and fixing

Sustainable Stormwater Stategies

  • Bioswale:

    • vegetated linear depression

    • cleanses, infiltrates stormwater

  • Porous Paving:

    • rock-filled reservoir, porous surface

    • cleanses, infiltrated stormwater

  • Rain Garden:

    • vegetated depression

    • cleanses, infiltrates stormwater

Treatment Plant

  • primary treatment: physical process: dense particles sink to the bottom of the tank

  • secondary treatment: biological process

    • bacteria degrade organic material, dissolved waste removed, bleaching (chlorine) to kill bacteria

  • possible tertiary treatment: UV light

Ocean as a Resource

  • expensive but sometimes the best option

  • high energy consumption + dangers to aquatic wildlife (high concentrated brine)