Water Resources

Usable Water is Rare

Groundwater Exists in pores (tiny spaces) within permeable rocks called aquifers Unconfined aquifers: water can easily flow in and out (ex. Rock covered by soil) Confined aquifers: impermeable layers surround aquifer, impeding water flow Water table: uppermost level at which water saturates rock – the ‘surface’ of groundwater Not the ‘water table’ I’m talking about 

Groundwater

Groundwater Groundwater Recharge: water from precipitation percolates downward and adds to aquifer Cannot recharge a confined aquifer unless there is an opening in the impermeable layer – recharge area

Groundwater Aquifers provide water for organisms Plant roots draw water up Springs: water from aquifer comes out at surface Dig wells down to aquifers Use pumps to work against gravity Artesian wells: confined aquifers under pressure, digging a well forces water up on it’s own

Groundwater Age of aquifer water / rate of recharge varies Unconfined aquifers (1 wk-1 yr) more likely to be contaminated with chemicals released by human activities than confined (10,000-20,000 yrs) Confined aquifers get used up faster (Ogallala aquifer) Cone of depression: wells withdraw water, depressing water table Saltwater intrusion: wells near coast draw saltwater into freshwater table

Surface Water Rivers/streams World’s largest rivers by volume: Amazon, Congo, Yangtze Humans settled near rivers – transportation and fertile ground (floodplains)

Surface Water Ponds/lakes Filled by precipitation, runoff, and groundwater flowing onto surface – depressions formed by tectonic activity or glaciation Oligotrophic: low productivity/nutrients Mesotrophic: medium productivity/nutrients Eutrophic: high productivity/nutrients

Surface Water Wetlands Absorb excess water, release it slowly, reducing flooding Saltwater mangrove swamps act as storm barricades Largest: Pantanal in S. America, Florida Everglades

Atmospheric Water Tiny but important percentage – rainfall distributes water around globe Droughts: prolonged periods without rain Can be worsened by human activity Kill organisms Disrupt nutrient cycling in soil “Dustbowl” conditions – dry soil blows away Hard, impermeable soil prevents water table recharge

Atmospheric Water Human activity increases risk of flooding Impermeable/impervious surfaces, such as pavement, prevent ground from soaking up water in storms

Checkpoint: What are the primary repositories of freshwater on Earth? Which is largest? What is the difference between a confined aquifer and an unconfined aquifer? How do their recharge rates differ? How do human activities worsen the effects of floods and droughts?

Altering the Availability of Water Some parts of Earth have less access to water Humans have invented a variety of methods to divert water from one place to another

Levees Enlarged bank built up on each side of a ricer to prevent flooding Humans build on floodplains, fertile soil – but don’t want to be flooded No more fertile sediment added Levees prevent floods at one location, but make floods worse beyond them New Orleans, Katrina

Dikes Similar to levees, built along ocean coasts Often combined with pumps to remove excess water

Dams Barrier that runs across a river/stream to control water flow Water stored behind dam in reservoir Hold water for consumption(40%), electricity generation (3%), flood control (18%), and recreation (38%)

Problems with Dams People behind dam forced to relocate Disruption of natural water flow to which organisms have adapted (ex. Migrating fish) Fish ladders: help fish bypass dams Some ecosystems depend on seasonal flooding

Aqueducts Canals or ditches used to carry water from one location to another Modern ones are enclosed to prevent evaporation New York and LA depend on aqueducts Problems: Construction is expensive/disruptive to ecosystems Decreases water at the source (can have international impacts)

Desalinization Removing salt from saltwater for water-poor countries Distillation Water is boiled, salt remains behind, vapor collected and condensed Very expensive Reverse osmosis Saltwater passed through thin semi-permeable membrane – water can pass, salt cannot Produces very salty liquid, called brine – disposal can harm local ecosystem

Checkpoint How do levees, dikes, dams, and aqueducts differ? What is the primary purpose of each? Why is it necessary to desalinize water? How does each method work? Which is more cost-effective?

Water Uses: Agriculture 70% of world’s freshwater Irrigation: Furrow irrigation: trenches dug between crop rows, water fills in Flood irrigation: entire field flooded at once Spray irrigation: like giant sprinklers Drip irrigation: hose w/ holes drips directly onto plants

Hydroponic Agriculture Cultivation of a crop in greenhouse conditions with their roots immersed in a nutrient-rich solution, but no soil Crops need less water, grown in ideal conditions year-round, with little to no pesticide

Water Uses: Industry Generation of electricity, cooling machinery, refining metals/paper Some processes do not use up water (turning turbines in dams) while others do (thermoelectric power plants releasing steam)

Water Uses: Households Varies heavily from country to country Average US citizen uses 157 gallons/day, average Kenyan uses 11 gallons/day

Water Uses: Households Flushing toilets, bathing, laundry, cooking/drinking, washing dishes, watering lawns, washing cars, filling swimming pools Over 1 billion people in the world lack access to clean drinking water

Checkpoint What are the dominant water uses by humans? How do different irrigation methods influence water use? What are the biggest steps you can take to reduce water wastage in your own home?

Water Ownership Having the right to use water is not the same as owning it Many disputes arise over who gets the water India vs. Bangladesh

Water Conservation Water is finite and must be shared Designing more efficient appliances Ex. Dual-flush toilets: two buttons, one uses 6 L for solid waste, other only uses 3 L, for liquid waste Designing more efficient manufacturing equipment Rainwater collection from impervious surfaces Wastewater for irrigation

Is the Water in Your Toilet Too Clean? The water in your toilet has been treated to drinking water safety standards, while water draining from your tub or washing machine is treated like sewage Gray water: wastewater from baths, showers, bathroom sinks, and washing machines No one wants to drink it, but it is suitable for watering lawns, washing cars, flushing toilets