Chapter 9 Section 2&3 Stream and Lakes PDF

11/13/2024 Chapter 9 Section 2 & 3 How is the process of rejuvenation in stream development explained? 1 ...

11/13/2024 Chapter 9 Section 2 & 3 How is the process of rejuvenation in stream development explained? 1  11/13/2024 How do freshwater lakes and wetlands form? Supply of Water Stream channels The region where water first accumulates to supply a stream is called the headwaters. Falling precipitation accumulates in small gullies at higher elevations and forms briskly moving streams. Copyright © McGraw-Hill Education Stream Development 2  11/13/2024 Supply of Water Stream channels Moving water carves a narrow pathway into the sediment or rock called the stream channel. Stream banks hold the moving water within them. When small streams erode away the rock or soil at the head of a stream, it is known as headward erosion. Copyright © McGraw-Hill Education Stream Development 3  11/13/2024 Supply of Water Stream channels The headward erosion of Stream A cuts into Stream B and draws away from its water into one stream, in a process called stream capture. Copyright © McGraw-Hill Education Stream Development Formation of Stream Valleys The energy of a stream comes from the movement of water down a slope. The slope of a stream channel is called the stream gradient. The gradient of the stream depends on its base level, which is the elevation at which it enters another stream or body of water. Copyright © McGraw-Hill Education Stream Development 4  11/13/2024 Formation of Stream Valleys The height of a stream above its base level determines how much downcutting energy the stream will have. Copyright © McGraw-Hill Education Stream Development Formation of Stream Valleys Meanders A bend or curve in a stream channel caused by moving water is called a meander. Water moving along the outside of a meander curve experiences the greatest velocity within the meander and erodes the side of the streambed. Copyright © McGraw-Hill Education Stream Development 5  11/13/2024 Formation of Stream Valleys Meanders Along the inside of a meander, the water moves more slowly and deposition is dominant. Copyright © McGraw-Hill Education Stream Development Formation of Stream Valleys Meanders After enough winding, it is common for a stream to cut off a meander and once again flow along a straighter path. The blocked-off meander becomes an oxbow lake, which eventually dries up. Copyright © McGraw-Hill Education Stream Development 6  11/13/2024 Visualizing Erosion and Deposition in a Meander The meanders of a stream are accentuated by differences in the velocity of water in the channel. Copyright © McGraw-Hill Education Stream Development Deposition of Sediment When streams lose velocity, they lose some of the energy needed to transport sediment, and deposition of sediment occurs. Copyright © McGraw-Hill Education Stream Development 7  11/13/2024 Deposition of Sediment Alluvial fans Alluvial fans are fan-shaped, sloping depositional features that form when water flows down steep slopes onto flat plains. Alluvial fans are composed mostly of sand and gravel. Copyright © McGraw-Hill Education Stream Development Deposition of Sediment Deltas The triangular deposit that forms where a stream enters a large body of water is called a delta. Delta deposits usually consist of layers of silt and clay particles. Copyright © McGraw-Hill Education Stream Development 8  11/13/2024 Rejuvenation During rejuvenation, a stream actively resumes the process of downcutting toward its base level. This causes an increase in the stream’s velocity, and the stream’s channel once again cuts downward into the existing meanders. Copyright © McGraw-Hill Education Stream Development Origins of Lakes Natural lakes, bodies of water surrounded by land, form in different ways in surface depressions and in low areas. Copyright © McGraw-Hill Education Lakes and Freshwater Wetlands 9  11/13/2024 Origins of Lakes Some lakes form when stream flow becomes blocked by sediment from landslides or other sources. Copyright © McGraw-Hill Education Lakes and Freshwater Wetlands Origins of Lakes Other lakes, such as moraine-dammed lakes, cirque lakes, and kettle lakes, have glacial origins. Copyright © McGraw-Hill Education Lakes and Freshwater Wetlands 10  11/13/2024 Lakes Undergo Change A depression that receives more water than it loses to evaporation or use by humans will exist as a lake for a long period of time. However, over geologic time, most lakes are temporary features. Copyright © McGraw-Hill Education Lakes and Freshwater Wetlands Lakes Undergo Change Freshwater wetlands A wetland is any land area that is covered with water for a part of the year. Wetlands include environments commonly known as bogs, marshes, and swamps, which have certain soil types and support specific plant species. Copyright © McGraw-Hill Education Lakes and Freshwater Wetlands 11  11/13/2024 Bogs Bogs are not stream-fed but instead receive their water from precipitation Marshes Freshwater marshes frequently form along the mouths of streams and in areas with extensive deltas. 12  11/13/2024 Swamps Swamps are low-lying areas often located near stream. Tend to contain larger plants Lakes Undergo Change Freshwater wetlands Wetlands play a valuable role in improving water quality. They serve as a filtering system that traps pollutants, sediments, and pathogenic bacteria contained in water sources. Copyright © McGraw-Hill Education Lakes and Freshwater Wetlands 13  11/13/2024 Lakes Undergo Change Freshwater wetlands The area of wetlands in the United States was drastically reduced until the 1980s. Since then, efforts have been made to preserve wetlands. Copyright © McGraw-Hill Education Lakes and Freshwater Wetlands 14  11/13/2024 Undergo Change Eutrophication The process by which bodies of water become rich in nutrients that stimulate excessive plant growth is called eutrophication. Copyright © McGraw-Hill Education Lakes and Freshwater Wetlands Undergo Change Eutrophication Although eutrophication is a natural process, it can be sped up with the addition of nutrients, such as fertilizers, that contain nitrogen and phosphorus. Copyright © McGraw-Hill Education Lakes and Freshwater Wetlands 15