Guided Notes on Lakes and Freshwater Wetlands, Section 9.3 1. A lake is a depression in the surface materials of a landscape that collects and holds water. 2. Lakes sometimes accumulate water from streams and runoff that flow into them. Lakes also receive water from local precipitation, springs, and other sources. 3. Most lakes have outlets from which water flows to rivers and to the ocean. 4. Oxbow lakes form when streams cut off meanders and leave isolated channels of water. Lakes can also form when stream flow becomes blocked by sediment from landslides. 5. Most of the lakes in Europe and North America are in recently glaciated areas. 6. Cirques carved high in the mountains by valley glaciers filled with water to form cirque lakes. 7. Blocks of ice left on the outwash plain ahead of melting glaciers eventually melted and left depressions called kettles. When these depressions filled with water, they formed kettle lakes. 8. Many lakes are found in areas where limestone is the dominant bedrock. 9. As groundwater percolating through limestone bedrock slowly dissolves calcium carbonate, it leaves holes in the limestone and forms caverns. 10. Lakes are temporary water-holding areas; over hundreds of thousands of years, lakes usually fill in with sediment and become part of a new landscape. 11. Through the process of photosynthesis, plants add oxygen and waste products to lake water. 12. The process by which lakes become rich in nutrients from the surrounding watershed, thereby resulting in a change in the kinds of organisms in the lake, is called eutrophication. 13. A wetland is a land area that is covered with water for a large part of the year. 14. Wetlands include environments commonly known as bogs, marshes, and swamps. 15. Bogs are not stream-fed, but instead receive their water from precipitation. The soils of bogs tend to be rich in Sphagnum, also called peat moss. The acidic soil of bogs supports unusual plant species, including insect-eating pitcher plants, sundew, and Venus’ flytrap. 16. Grasses, reeds, sedges, and rushes, along with abundant wildlife, are common in marsh areas. 17. Swamps may develop from marshes that have filled in sufficiently to support the growth of shrubs and trees. 18. Wetlands serve as a filtering system that traps pollutants, sediments, and pathogenic bacteria contained in water sources. Wetlands also provide vital habitats for migratory waterbirds and homes for an abundance of other wildlife.