© 2011 Pearson Education, Inc. AP Environmental Science Mr. Grant Lesson 72 Human Activities Affect Waterways

© 2014 Pearson Education, Inc. Mastery Check Describe three benefits and three costs of damming rivers. Damming can generate electricity, control flooding, and provide a reliable source of water for human consumption and irrigation. It can also alter or destroy habitat, displace people, and cause floods if the dam fails.

© 2011 Pearson Education, Inc. Objectives: Define the term sinkhole. Discuss how we use water and alter freshwater systems. TED - With wisdom and wit, Anupam Mishra talks about the amazing feats of engineering built centuries ago by the people of India's Golden Desert to harvest water. These structures are still used today -- and are often superior to modern water megaprojects.

© 2011 Pearson Education, Inc. Sinkhole: Define the term sinkhole.

© 2011 Pearson Education, Inc. Discuss how we use water and alter freshwater systems. Water is a renewable but limited resource, so we must manage it sustainably. We use water for agriculture, industry, and residential use. Globally 70% is used for agriculture. We pump water from aquifers and surface water bodies, sometimes at unsustainable rates. Some of our water extraction now goes to bottled water, which is hugely popular even though it is no healthier than tap water and creates substantial plastic waste. We attempt to control floods with dikes and levees.

© 2011 Pearson Education, Inc. Discuss how we use water and alter freshwater systems, con’t. We divert water with canals and irrigation ditches to bring water to where it is desired. We have dammed most of the world’s rivers. Dams bring a diversity of benefits and costs. Some dams are now being removed. Many wetlands have been lost, and we are now trying to restore some.

© 2014 Pearson Education, Inc. Human Activities Affect Waterways  Water is crucial for human health as well as farms and factories  Water is a limited but renewable resource  Withdrawal of water in most of the world is unsustainable  We are depleting many sources of surface water and groundwater  One-third of the world’s people are affected by water shortages

© 2014 Pearson Education, Inc. Human Activities Affect Waterways  We have achieved impressive engineering accomplishments to harness fresh water  60% of the world’s largest 227 rivers have been strongly or moderately affected by dams, dikes, and diversions

© 2014 Pearson Education, Inc. Fresh water and human populations are unevenly distributed across Earth  Different areas possess different amounts of water  People are not distributed in accordance with water availability  Asia has the most water of any continent but the least water available per person  Densely populated nations like Pakistan, Iran, India, and Egypt face serious water shortages  Fresh water is also unevenly distributed in time  Seasonal rains lead to differences in water availability  India can receive half of its rain in a single monsoon  Dams are used to store water for dry times

© 2014 Pearson Education, Inc.

Fresh water and human populations are unevenly distributed across Earth  Climate change will worsen conditions in many regions  Altered precipitation patterns  Melting glaciers causing early season runoff  Intensified droughts and flooding  One-third of the world’s major rivers experienced reduced flow from 1948 to 2004  Attributed largely to climate change

© 2014 Pearson Education, Inc. Water supplies households, industry, and especially agriculture  Globally, 70% of water is used for agriculture, 20% for industry, and 10% for residential and municipal use  Arid countries use more water for agriculture  Developed countries use more water for industry

© 2014 Pearson Education, Inc. Water supplies households, industry, and especially agriculture  Consumptive use  when water is removed from an aquifer or surface water body and is not returned  Nonconsumptive use  does not remove, or only temporarily removes, water Irrigation = is the water applied to crops Electricity generation at hydroelectric dams

© 2014 Pearson Education, Inc. Water supplies households, industry, and especially agriculture  Rapid population growth requires more food and clothes  We use 70% more irrigation water than 50 years ago  Irrigation can more than double crop yields  18% of land is irrigated but produces 40% of our crops  Irrigation is highly inefficient  Water evaporates in “flood and furrow” irrigation  Overirrigation leads to waterlogging and salinization  Reducing world farm income by $11 billion

© 2014 Pearson Education, Inc. Governments subsidize irrigation Farmers in California’s Imperial Valley pay only 1 penny for 220 gallons of water Water use for agriculture is subsidized by governments Farmers have little incentive to conserve

© 2014 Pearson Education, Inc. Excessive water withdrawals can drain rivers and lakes  In many places, we are withdrawing water at unsustainable rates  Many of the world’s major rivers regularly run dry before reaching the sea  The Colorado River often does not reach the Gulf of California, threatening the future of cities and farms that rely on its water  Reduced flow drastically changes the river’s ecology and plant community and destroys fish and invertebrates

© 2014 Pearson Education, Inc. Excessive water withdrawals can drain rivers and lakes  The Aral Sea in in present day Uzbekistan and Kazakhstan was once the fourth-largest lake on Earth  It lost 80% of its volume in 45 years  The two rivers leading into the Aral Sea were diverted to irrigate cotton fields  60,000 fishing jobs are gone  Pesticide-laden dust is blown into the air  Little cotton can grow on the salty soil

© 2014 Pearson Education, Inc. The Aral Sea

© 2014 Pearson Education, Inc. Excessive water withdrawals can drain rivers and lakes  Worldwide, 15%–35% of water withdrawals for agriculture are unsustainable  Water mining  withdrawing water faster than it is replenished

© 2014 Pearson Education, Inc. Groundwater can also be depleted Groundwater is more easily depleted than surface water  Aquifers recharge slowly  Used by one-third of all people As aquifers are mined, water tables drop  In many areas, water tables are falling 1–3 m/year  Salt water intrudes in coastal areas, making water undrinkable  Land above the aquifers subsides

© 2014 Pearson Education, Inc. Groundwater can also be depleted  Sinkholes  areas where ground gives way suddenly  Once the soil is compacted, aquifers can’t recharge  Wetlands that get their water from groundwater dry up

© 2014 Pearson Education, Inc. Groundwater supplies our bottled water  Groundwater is being withdrawn for use as bottled water  An average American drinks 29 gallons/year  Sales topped $15 billion in the United States in 2012  People drink bottled water for portability, convenience  They think it tastes better or is healthier  Bottled water is no better than tap water  It is heavily packaged and travels long distances using fossil fuels  Energy costs of bottled water are 1000–2000 times greater than those of tap water  Only 25% of bottles are recycled in the United States

© 2011 Pearson Education, Inc. Bottled water is popular but problematic Energy costs of bottled water are 1,000–2,000 times greater than those of tap water

© 2014 Pearson Education, Inc. People build dikes and levees to control floods  Flooding  a normal, natural process where water spills over a river’s banks  Spreading nutrient-rich sediments over large areas  In the short term, floods damage property  Levees (or dikes) are the long, raised mounds of earth along the banks of rivers that hold water in channels  Stop flooding from most rains  May make floods worse by forcing water to stay in channels, build energy, and then overflow  Dams prevent flooding and change a river’s nature  Releasing water periodically simulates flooding

© 2011 Pearson Education, Inc. We build dikes and levees to control floods

© 2011 Pearson Education, Inc. Levees increase flooding A major levee along the Mississippi River failed after Hurricane Katrina, allowing parts of New Orleans to be flooded

© 2014 Pearson Education, Inc. We divert surface water to suit our needs  People divert water to farm fields, homes, and cities  Water from the Colorado River is diverted to Denver, Las Vegas, Los Angeles, and elsewhere  In China, $62 billion is being spent to move water from the Yangtze to the Yellow River  Politically strong, water-poor areas forcibly take water from weaker communities  Los Angeles commandeered water from rural areas, turning the environment into desert, creating dustbowls, and destroying the economy  In 1941, it diverted streams that fed Mono Lake  Lake levels fell; salt concentrations doubled

© 2011 Pearson Education, Inc. Water-poor regions take water from others

© 2011 Pearson Education, Inc. We divert surface water for our needs The once mighty Colorado River has been extensively diverted and used

© 2014 Pearson Education, Inc. We have erected thousands of dams  Dam  any obstruction placed in a river or stream to block the flow of water  They create reservoirs  artificial lakes  Dams are built to prevent floods, provide drinking water, allow irrigation, and generate electricity  45,000 large dams have been erected in more than 140 nations  Tens of thousands of smaller dams have been built  Only a few major rivers remain undammed in remote regions of Canada, Alaska, and Russia

© 2011 Pearson Education, Inc. We have erected thousands of dams

© 2011 Pearson Education, Inc. A typical dam

© 2014 Pearson Education, Inc. We have erected thousands of dams  Dams produce a mix of benefits and costs  The dam on the Yangtze River is the largest in the world  Its reservoir stretches for 616 km (385 mi)  It provides flood control, passage for boats, and huge amounts of electricity

© 2014 Pearson Education, Inc. We have erected thousands of dams However, it cost $39 billion to build  Flooded 22 cities and the homes of 1.24 million people  Submerged 10,000-year-old archaeological sites  Drowned farmland and wildlife habitat  The tidal marshes at the Yangtze’s mouth are eroding  Pollutants may be trapped, making the water undrinkable

© 2014 Pearson Education, Inc. Some dams are being removed  Some people feel that the costs of dams outweigh their benefits and are pushing to dismantle dams  Removing dams will restore riparian ecosystems, reestablish fisheries, and revive river recreation  The Federal Energy Regulatory Commission (FERC) renews licenses for dams  If dam costs exceed benefits, the license may not be renewed  400 dams have been removed in the United States  Some property owners who opposed the removal changed their minds once they saw the healthy river

© 2014 Pearson Education, Inc. Wetlands are affected by human manipulations of waterways  Wetlands are being lost as we divert and withdraw water, channelize rivers, build dams, etc.  Wetlands have also been widely drained for agriculture  As wetlands disappear, we lose ecosystem services  Filtering pollutants, wildlife habitat, flood control, etc.  Many are trying to protect and restore them

© 2014 Pearson Education, Inc. Wetlands are affected by human manipulations of waterways  The Ramsar Convention on Wetlands of International Importance (1971) seeks the conservation and wise use of wetlands in the context of sustainable development  1900 sites covering 185 million ha are protected

© 2014 Pearson Education, Inc. Solutions to Depletion of Fresh Water  Our use of fresh water has doubled over the last 50 years  We can either increase supply or reduce demand  Increasing supply through intensive extraction is only a temporary fix  Diversions increase supply in one area but decrease it elsewhere

© 2011 Pearson Education, Inc. TED Video To promote smart water management, Anupam Mishra works to preserve rural India’s traditional rainwater harvesting techniques. "In [him] lives a spirit, of quiet service, that once existed freely in our politics and our activism, a spirit that has been completely excised from one sphere and remains gravely threatened in the other." Ramachandra Guha, in The Hindu Anupam Mishra: The ancient ingenuity of water harvesting (17:15)