© 2011 Pearson Education, Inc. AP Environmental Science Mr. Grant Lesson 74 Freshwater Systems

© 2011 Pearson Education, Inc. Objectives: Define the term aquifer. Explain water’s importance to people and ecosystems, and describe the distribution of fresh water on earth. Describe major types of freshwater systems.

© 2011 Pearson Education, Inc. Aquifer: A wet underground layer of water- bearing permeable rock or unconsolidated materials (gravel, sand, silt, or clay) from which groundwater can be usefully extracted using a water well. Define the term aquifer.

© 2011 Pearson Education, Inc. Explain water’s importance to people and ecosystems, and describe the distribution of fresh water on earth. Water is a renewable but limited resource, so we must manage it sustainably. A functioning water cycle is vital to maintaining our civilization and the natural systems that support it. Of all the water on Earth, only about 1% is readily available for our use. Water availability varies in space and time, and regions vary greatly in the amounts they possess. Climate change may bring water shortages in some regions.

© 2011 Pearson Education, Inc. Gambling with water in the Colorado River basin 7 states share the Colorado river Droughts and overuse are threatening supplies Las Vegas, Nevada, needs more water than it is allotted Other states will let Las Vegas drill for underground water Drilling threatens the area’s ecology and people This issue will end up in Nevada’s Supreme Court

© 2011 Pearson Education, Inc. The Colorado River The Colorado River originates in the Rocky Mountains -Draining into the Gulf of California Its waters chiseled the Grand Canyon -But it has been reduced to a mere trickle Dams provide flood control, recreation, and hydroelectric power -30 million people use the water

© 2011 Pearson Education, Inc. Freshwater systems Water may seem abundant, but drinkable water is rare Freshwater = relatively pure, with few dissolved salts -Most is tied up in glaciers, ice caps, and aquifers

© 2011 Pearson Education, Inc. Water is renewed and recycled As water is cycled it redistributes heat, erodes mountains, builds river deltas, maintains ecosystems and organisms -It also shapes civilizations and political conflicts Surface water = on Earth’s surface -1% of freshwater Runoff = water that flows over land -Water merges in rivers and ends up in a lake or ocean Tributary = a smaller river slowing into a larger one Watershed (drainage basin) = the area of land drained by a river system (river and its tributaries)

© 2011 Pearson Education, Inc. Water is renewed and recycled as it moves through the hydrologic cycle

© 2011 Pearson Education, Inc. Water Cycle Scramble

© 2011 Pearson Education, Inc. Groundwater plays a key role Groundwater = water beneath the surface held in pores in soil or rock -20% of the Earth’s freshwater supply Aquifers = porous, sponge-like formations of rock, sand, or gravel that hold water -Zone of aeration = pore spaces are partly filled with water -Zone of saturation = spaces are filled with water -Water table = boundary between the two zones Recharge zone = any area where water infiltrates Earth’s surface and reaches aquifers

© 2011 Pearson Education, Inc. A typical aquifer

© 2011 Pearson Education, Inc. There are two categories of aquifers Confined (artesian) aquifer = water-bearing, porous rocks are trapped between less permeable substrate (clay) layers -Is under great pressure Unconfined aquifer = no upper layer to confine it -Readily recharged by surface water Groundwater’s average age is 1,400 years -It may be tens of thousands of years old Groundwater becomes surface water through springs or human-drilled wells

© 2011 Pearson Education, Inc. The Ogallala Aquifer The world’s largest known aquifer Underlies the Great Plains of the U.S. Its water has allowed farmers to create the most bountiful grain-producing region in the world

© 2011 Pearson Education, Inc. Water is unequally distributed across Earth Water is unevenly distributed in space and time -Different areas possess different amounts of water -People erect dams to store water Many densely populated areas are water-poor and face serious water shortages

© 2011 Pearson Education, Inc. Climate change may bring shortages Climate change will cause -Altered precipitation patterns -Melting glaciers -Early season runoff -Intensified droughts -Flooding Lake Mead is already hurting from drought

© 2011 Pearson Education, Inc. Describe major types of freshwater ecosystems. A watershed is the area of land drained by a river system. The main types of freshwater ecosystems include rivers and streams, lakes and ponds, and wetlands.

© 2011 Pearson Education, Inc. Rivers and streams wind through landscapes Rivers shape the landscape Braided river = an interconnected series of watercourses that run through steep slopes Meandering river = rivers in flatter areas -Water rounding a bend erodes soil from the outer bank -Sediment is deposited on the inside of the bend -Rivers become exaggerated oxbows

© 2011 Pearson Education, Inc. Rivers shape the landscape Oxbows = areas where river bends become exaggerated Oxbow lake = erosion cuts off and isolates the oxbow into a U-shaped water body

© 2011 Pearson Education, Inc. A river may shift course over time Floodplain = areas nearest to the river’s course that are flooded periodically -Frequent deposition of silt makes floodplain soils fertile -Good areas for agriculture Riparian = riverside areas that are productive and species-rich Rivers and streams hosts diverse ecological communities -Algae, insects, fish, amphibians, birds, etc.

© 2011 Pearson Education, Inc. Lakes and ponds are ecologically diverse Lakes and ponds = bodies of open, standing water Littoral zone = region ringing the edge of a water body -Rooted aquatic plants grow in this shallow part Benthic zone = extends along the bottom of the water body -Home to many invertebrates Limnetic zone = open portion of the lake or pond where sunlight allows photosynthesis Profundal zone = water that sunlight does not reach -Supports fewer animals because there is less oxygen

© 2011 Pearson Education, Inc. A typical lake

© 2011 Pearson Education, Inc. Lakes vary in their nutrients and oxygen Oligotrophic lakes and ponds = have low nutrient and high oxygen conditions Eutrophic lakes and ponds = have high nutrient and low oxygen conditions Eventually, water bodies fill completely in through the process of succession The largest lakes are known as inland seas -Great Lakes, The Caspian Sea

© 2011 Pearson Education, Inc. Wetlands include marshes, swamps, bogs, and seasonal pools Wetlands = the soil is saturated with shallow standing water Freshwater marshes = shallow water -Plants grow above the surface Swamps = shallow water in forested areas -Can be made by beavers Bogs = ponds covered in thick floating mats of vegetation -A stage in aquatic succession Species in vernal pools are adapted to seasonal drying

© 2011 Pearson Education, Inc. Wetlands are valuable Wetlands are extremely valuable for wildlife -They slow runoff, reduce flooding, recharge aquifers, and filter pollutants People have drained wetlands, mostly for agriculture -Southern Canada and the U.S. have lost over half of their wetlands In 2006 the Supreme Court told the Army Corps of Engineers it must create guidelines to determine when wetlands are valuable enough to protect by law