Environmental Science and Sustainability - Ch9 PDF

CHAPTER 9 Land: How Does It Shape Us? Copyright © 2023 W. W. Norton & Company, Inc. Chapter 9 Outline 9.5 What Is Soil, and Where Does It Come From? 9.6 What Makes Soil Alive? 9.7 How Can Humans Repair and Sustain the Land? Chapter Objectives: This chapter will help you… describe how rock...

CHAPTER 9 Land: How Does It Shape Us? Copyright © 2023 W. W. Norton & Company, Inc. Chapter 9 Outline 9.5 What Is Soil, and Where Does It Come From? 9.6 What Makes Soil Alive? 9.7 How Can Humans Repair and Sustain the Land? Chapter Objectives: This chapter will help you… describe how rocks and minerals form and some of their uses. discuss how soils form and how soil-dwelling organisms and soil characteristics affect water infiltration, soil fertility, and plant growth. explain how human activities can degrade or restore the land. “We know more about the movement of celestial bodies than about the soil underfoot.” —Leonardo da Vinci Earth’s surface is a dynamic place with forces at and below the surface that can shift the ground beneath our feet. Topsoil and beach erosion are more gradual changes to Earth’s surface. Climate change is also resulting in sea level rise, which accelerates erosion along shores. 9.5 What Is Soil, and Where Does It Come From? (1 of 2) Soil can be considered Earth’s skin, but soil is much thinner than skin relative to the size of Earth. Soil is a complex mixture of weathered rock and mineral particles (sediment), dead and decaying plant and animal matter, and the multitude of organisms that live within these materials. Soil is created by processes at Earth’s surface, where the lithosphere (rocks) and the biosphere (life) interact, breaking down geologic source or parent material into particles. What Is Soil, and Where Does It Come From? (2 of 2) Air spaces around particles in a soil allow water to move down into the soil in a process called infiltration. Larger spaces of air in the soil promote aeration. Smaller particles pack together and influence infiltration and nutrient retention. Mixtures of particle sizes, types of parent material, soil organisms, and organic matter all determine a soil’s structure and texture. Soil texture affects plant growth. Soil Horizons (1 of 2) The action of living (biotic) and nonliving (abiotic) factors in the soil creates layers known as soil horizons. A soil profile, the collection of soil horizons at a location, is a cutaway view of the soil and is composed of up to four soil horizons: O, A, B, and C. Soil profiles are typically less than 3 feet deep. Soil Horizons (2 of 3) Topsoil is the uppermost 2–6 inches of soil and contains the O and A horizons, which have a complex mixture of materials that include organic matter derived from living things. The O horizon is made up of fallen leaves and dead organic matter called detritus. The A horizon is a mixture of mineral fragments and organic matter. Water infiltrates through this layer. Soil Horizons (3 of 3) The B horizon is the subsoil that is composed of mineral matter. The lowest horizon, the C horizon, is composed of weathered parent material, also known as rock or sediment. Take-Home Message Soil is a thin, complex mixture of materials and organic matter that forms on Earth's surface. Soil is arranged into layers called horizons. Soil consists of mineral particles weathered from the rock cycle, dead and decaying plant and animal matter, and the many organisms that live in this material. 9.6 What Makes Soil Alive? (1 of 2) Soil is rich with life and supports communities of animals, microorganisms, insects, and worms. Tiny nematode worms live in upper levels of the soil’s A horizon in numbers exceeding 100,000 per cup of soil, while consuming food and excreting nutrients. Each nematode like the one shown here consumes thousands of bacteria per minute and excretes nutrient-rich micro- manure. 9.6 What Makes Soil Alive? (2 of 2) Earthworms pull material from the surface as they burrow through soil, digesting and mixing soil and organic material, resulting in rich excrement known as castings. Other microorganisms living in the soil are bacteria and fungi. One cup of topsoil containing more total microorganisms than the number of people living on Earth. Microorganisms speed the decomposition of organic matter, releasing CO2 and producing vital molecules that plants can take back up and reuse. Organic Matter and Soil Structure Some complex organic compounds are resistant to being broken down, which can result in soil called humus, a complex, dark, sticky organic material that can remain relatively stable over time. Humus allows for a high degree of water and nutrient retention. Soil Classification and Factors Affecting Soil Formation (2 of 3) Biomes are linked to specific soil orders. For example, deserts such as the Mojave in the southwestern United States exist on thin, light covered porous soils often without an O horizon. Topsoil and Plant Growth For successful plant growth to occur, a delicate balance must exist between the water, pore space, nutrients, and root space in the soil. These properties are called tilth, the overall structure and conditions that facilitate plant growth. When topsoil forms faster than it erodes, it thickens and supports more plant growth, but when erosion thins soils, the opposite occurs. The US Department of Agriculture estimates that it takes centuries to produce an inch of topsoil. Water in Topsoil (1 of 2) Plants consume water in the soil by transporting it from the roots up through the plant to the leaves, where photosynthesis occurs. Even if enough water is applied to soils for plant growth, the characteristics of the soil must be conducive to water retention. Water in Topsoil (2 of 2) Plant growth can be inhibited by salinization, which is when water evaporates, and salts build up in the soil enough to impact plant growth. Water can also carry nutrients away from plants through leaching, a process driven by water in which mineral elements are moved down to deeper soil layers, potentially beyond the reach of plant roots, to be carried away in groundwater or stream flow. Take-Home Message A variety of organisms live in the soil, and there is a great diversity within soils. Topsoil refers to the uppermost layers of soil. The amount of water in this soil is a crucial factor for plant growth. Erosion can quickly remove topsoil that has taken centuries to build. Plant growth depends on the structure of soil, as well as the balance of aeration, water retention, and nutrient availability. 9.7 How Can Humans Repair and Sustain the Land? Earth processes like plate tectonics or erosion are inevitable, and humans can attempt to adapt to or to mitigate the impacts. Human actions can also degrade the land, with some forms of degradation, such as soil degradation and erosion, occurring as a side effect of certain farming practices. Degraded landscapes can be rehabilitated or restored after human use. Agriculture and Grazing (1 of 2) Farming practices, although increasingly productive, often accelerate soil erosion and degrade soil fertility. Tillage, preparing the soil for planting by breaking it up and turning it over with a plow, provides effective weed control, but exposes the soil to wind and water erosion Overuse of pesticides, herbicides, or fertilizers, overirrigation, and overgrazing can also damage land. Generations of overgrazing by livestock can create deserts, in a processed called desertification. Agriculture and Grazing (2 of 2) Sustainable agricultural practices can enhance soil production and build soil quality. Terracing can turn steep slopes into a series of flat steps that dramatically reduce soil erosion. Planting ground cover like hedgerows and cover crops can maintain soil, while adding organic fertilizer can boost soil fertility. Grazing can also be made sustainable by rotating livestock to new areas, allowing time to restore degraded soils. The Erosion of Civilizations Plowing leaves the soil bare and exposed to erosion. Plow-based farming was only sustainable among ancient civilizations that lived on flat- lying floodplains and deltas, such as floodplains along the Nile, Tigris, and Indus rivers, and of rivers in lowland China. When Romans used plow-based farming on upland slopes, it eventually eroded the areas down to the bedrock. Mining Mining practices are not considered to be sustainable, but abandoned mine sites can be reclaimed and rehabilitated to improve their ecological value. Rehabilitative measures include importing topsoil, planting trees, and sustainable livestock grazing. Globally, mines in Mongolia, the European Union, and China have been successfully rehabilitated. The Eden Project, which is the world’s largest greenhouse and center of environmental education, was created from reclaimed clay mines in Cornwall, England. Forestry Humans are causing deforestation at a global annual rate of 13 million hectares per year due to logging or burning. Removing trees removes the primary source of an area’s organic material and the soil- binding ability of tree roots. Tree harvesting from steep slopes also leaves land susceptible to landslides following rain events and rapidly eroding topsoil. Sustainable forest management can reduce the impacts of forestry practices, which includes soil loss. Urbanization In the face of growing human populations, urban areas have begun reclamation programs of contaminated or abandoned industrial sites, which are called brownfields. Sustainable building practices, like rain gardens and landscaping, encourage rainwater infiltration which can reduce runoff. Creating city green spaces and walkable streets encourages people to get outside and better appreciate sustainable practices. Successful and sustainable urban planning projects involve economic and political choices about how our values influence land use. Take-Home Message Land uses such as farming and grazing, mining, forestry, and urban development can have an enormous negative impact on the land. However, regenerative agricultural practices can enhance rather than degrade soil fertility. While mining, forestry, and urbanization impact landscapes, their effects can be mitigated to varying degrees by changes in practices or restoration efforts. Question 1 Which of the following is true about leaching? A. It is an artificial method to help plant growth. B. It is caused by movement of water upward through soil from the water table. C. It adds nutrients from the air to the soil. D. It removes water-soluble nutrients from topsoil. Question 1 Answer Which of the following is true about leaching? A. It is an artificial method to help plant growth. B. It is caused by movement of water upward through soil from the water table. C. It adds nutrients from the air to the soil. D. It removes water-soluble nutrients from topsoil. (Correct) Question 2 The O horizon is _________________________________________________. A. composed of equal amounts of bedrock and organic material. B. primarily loam. C. usually more sand than silt or clay. D. primarily composed of organic materials that contribute to topsoil formation. Question 2 Answer The O horizon is _________________________________________________. A. composed of equal amounts of bedrock and organic material. B. primarily loam. C. usually more sand than silt or clay. D. primarily composed of organic materials that contribute to topsoil formation. (Correct) Question 3 Terracing, using cover crops, and rotational grazing all ______________________. A. are techniques for conserving soil resources and fertility. B. contribute to leaching. C. contribute to erosion and desertification. D. are prohibited in organic farming. Question 3 Answer Terracing, using cover crops, and rotational grazing all ______________________. A. are techniques for conserving soil resources and fertility. (Correct) B. contribute to leaching. C. contribute to erosion and desertification. D. are prohibited in organic farming. Question 4 Which of the following is a consequence of clearing forests for agricultural purposes? A. The soil becomes richer and retains moisture better because there are few trees to take up the water and soil nutrients. B. Soil erosion increases because the tree roots and other vegetation that stabilize the soil have been removed. C. Water runoff decreases because crops will take up more of the moisture. D. CO2 levels in the atmosphere drop to dangerously low levels. Question 4 Answer Which of the following is a consequence of clearing forests for agricultural purposes? A. The soil becomes richer and retains moisture better because there are few trees to take up the water and soil nutrients. B. Soil erosion increases because the tree roots and other vegetation that stabilize the soil have been removed. (Correct) C. Water runoff decreases because crops will take up more of the moisture. D. CO2 levels in the atmosphere drop to dangerously low levels. Credits This concludes the Lecture PowerPoint presentation for Environmental Science and Sustainability, Chapter 9, by David Montgomery and Daniel Sherman For more resources, please visit https://digital.wwnorton.com/environsci2 Copyright © 2023 W. W. Norton & Company, Inc.