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Water Resources Chapter 9 Water, water, everywhere… • Most (97%) of Earth’s water is saltwater • Of the 3% that is freshwater, <1% is available for us • The rest is frozen or deep underground Groundwater • Aquifer – groundwater is located in small spaces within permeable layers of rock and sediment • Unconfined aquifer – porous rock + soil; water can move in and out freely • Confined aquifer – surrounded by impermeable layers – Springs or artesian wells Groundwater… • Water table – the uppermost level of water saturation in the soil • Groundwater recharge – water from precipitation that percolates back into the soil Groundwater… • Pumping water out of the ground faster than it can be recharged will cause a drop in the water table • Wells near the coastline can suffer from saltwater intrusion as the freshwater is infiltrated with ocean water Surface Water • Streams, rivers, ponds, lakes, wetlands • 3 largest rivers based on volume: 1. Amazon in South America 2. Congo in Africa 3. Yangtze in China • Human settlement and impacts – Transportation – Irrigation – Agriculture Surface water… • Lakes – surface area versus depth and volume determine size • Classification of lakes: 1. Oligotrophic • Low nutrient levels = low productivity 2. Mesotrophic • Moderate productivity 3. Eutrophic • Highly productive Surface water… • Wetlands – help to offset flooding during periods of heavy rainfall • Also are very useful at absorbing pollutants Atmospheric water • Drought – lack of rainfall – Harm ecosystems and humans – Also impact soil: • Harder for nutrients to cycle • Dried soil more vulnerable to wind erosion • Flooding – too much rainfall – Also cause crop and property damage – Ground has been paved • Excess water can’t soak in Humans alter water availability • Flood control/prevention: – Levees • • • • • Mississippi River (New Orleans) Black Warrior River (Northport) Floodwaters move downstream Encourages development of floodplain Risk of collapse or breach – Dikes • Levees for ocean waters • The Netherlands Humans alter water availability… • Dams – cross rivers to produce a reservoir – Water used for consumption, generation of electricity, flood control, recreation – Environmental issues: • Disrupt ecosystems during construction • Interfere with natural flow of water • Silt behind the dam Humans alter water availability… • Aqueducts – carry water to another place – New York City & Los Angeles – Environmental issues • Disruption of ecosystem during construction • Less water available in ecosystem feeding the aqueduct • Can cause international disputes Humans alter water availability… • Desalination – making saltwater fresh – Distillation: boiled water leaves salt behind, steam is captured and cooled to condense • Requires a lot of energy – Reverse osmosis: water is forced through a membrane which blocks the salt • More efficient and less costly • Brine – super salty water waste Water use • Agriculture – Irrigation: considerations – cost, amount of evaporation • • • • Furrow ~ 65% efficient Flood ~ 70-80% efficient Spray ~ 75-95% efficient Drip > 95% – Hydroponic agriculture Water Use… • Industry – Electrical generation: • In the U.S. ~ ½ of all water used goes toward generating electricity • Hydroelectric generation returns water to source • Thermoelectric power plants use water to cool the system and it leaves as water vapor – Refining metals and making paper • Gallons used per kg made: • Copper 116, Aluminum 108, Steel 68, paper 33 Water Use… • Households ~ 10% of all water used in U.S.