1 8.4 Lakes and Groundwater Most of the earth’s lakes are in the northern hemisphere at high latitudes. Canada has more than half of the world’s lakes.

2 Freshwater is only 3% of Earth’s water and only.0071% is surface water. a. Lentic - standing water such as lakes and ponds Surface freshwater is further grouped into: b. Lotic - running water such as rivers, tributaries, creeks, and streams

3 Lakes are lentic bodies of freshwater surrounded by land. Water fills in surface depressions and a lake develops. Russia’s Lake Baikal is the world’s oldest and deepest lake at 5,000 ft. (#8) * numbers indicate rank by size

4 Seas are smaller, partially enclosed areas of ocean or inland waters if they contain saltwater. Caspian Sea is the largest lake. (#1)

5 The Caspian Sea is 5x larger than Lake Superior and has 130 rivers that flow into it. The Caspian is the remains of the Tethys Ocean trapped inland by plate tectonics some ~50 m.y.a. It is 1/3 less salty than the ocean. The Caspian is famous for its unique fish, the Beluga Sturgeon, highly valued for its caviar. All 3 species of sturgeon are protected by the CITES treaty.

6 (#2) Superior largest U.S. lake. (#4) Huron (#5) Michigan Erie Ontario The Great Lakes contain 22% of the world’s fresh surface water. The St. Laurence Seaway, opened in 1959, connects the Lakes to the Atlantic.

7 (#3) Lake Victoria lies in the western part of Africa's Great Rift Valley and is the source of the White Nile, the longest branch of the Nile River. Lake Tanganyika (#5) is the second deepest lake and is home to 250 species of Cichlids. Lake Chad was the #6 largest lake but has shrunk to 10% of its original size from drought and over-drafts for agriculture.

8 # 6. The Aral Sea was once part of the same Tethys Ocean as the Caspian. It was the world's fourth-largest inland sea until the Soviet Union began diverting its water for irrigation projects in the 1960s. As the sea dried up to less than half its former size, the increased salinity killed most of the vegetation and destroyed the fishing industry. The Aral Sea is also heavily polluted from weapons testing, wind- blown salts, industrial and agricultural run-off. The water is polluted and dust-laden air are causing serious public health problems.

9 Lentic water is divided into 3 horizontal zones: a. littoral zone - shoreline vegetation b. limnetic zone - water’s surface in the lake’s center c. profundal zone - dark area at the bottom; without photosynthesis Water is mixed by seasonal changes in temperature with colder denser water near the surface in winter. The surface may freeze leaving animals who can survive in the cold, oxygen river water below the ice.

10 As lakes age, the beds fill in with nutrients and become more shallow. Lakes are temporary parts of the landscape and eventually will fill in with nutrients and vegetation, changing into a meadow or forest. Young lakes have steeply sloping shorelines with deeper beds - called oligotrophic lakes.

11 Types of groundwater are: 1. An aquifer is a pocket of freshwater trapped under ground. Graphic: St. Johns River Water Management District Ogallala aquifer is the world's largest aquifer. Groundwater in large aquifers is the main source of drinking water and irrigation. As precipitation percolates into the soil, it is cleaned of many pollutants.

12 The volume of water in underground reservoirs is 4 times the volume of water in the Great Lakes. The aquifer is recharged by rainfall but at 25% of the rate that it is being used. If water is withdrawn at a faster rate than it can be replenished, a draw down of the water table occurs, resulting in decreased hydrostatic pressure. When salt water seeps under lower density freshwater and pollutes the well or aquifer, it is called saltwater intrusion. It is usually irreversible and prevents using the water for drinking

13 2. Springs can discharge water into the aquifer or surface water. Springs are graded by the amount of water they emit. Florida’s Silver Spring is the world’s largest spring. Wakulla Spring, FL is the deepest spring at 185 feet. Artesian springs (wells) emit water without pumping.

14 3. Geysers form when a vent from a deep aquifer is constricted - twisted, crooked or angled. Water heated by magma builds up steam and pressure until it erupts. “Old Faithful” in Yellowstone National Park, (ID, MT, WY) erupts at hourly intervals sending nearly 12,000 gallons of boiling water to 130 feet in the air.

15 4. Karst caves are the most common inland caves. Water reacting with carbon dioxide forms carbonic acid that slowly dissolves through limestone bedrock. The water table drops making streams that cut new underground tunnels. Caves are like a giant plumbing systems.

16 Kentucky’s Mammoth Cave is by far the world’s longest cave system with a subterranean drainage basin covering more than 400 square miles. It was declared an International Biosphere Reserve in 1990.

17 Caves are home to many unusual species including eyeless fish, and unusual geological structures such as stalactites and stalagmites. NPS

18 A cavern is a group of huge underground chambers - often unconnected. Decaying organic matter buried for ages in the ground can emit hydrogen sulfide gas. If the gas dissolves in groundwater and mixes with oxygen, a sulfuric acid solution is formed that cuts the rock.