(19) Environmental Science



What Is Biodiversity and Why Is It Important?

CONCEPT 3-4A The biodiversity found in the earth’s genes, species, ecosystems, and ecosystem processes is vital to sustaining life on the earth.

CONCEPT 3-4B Soil is an important component of biodiversity that supplies most of the nutrients needed for plant growth and helps purify and store water and control levels of carbon dioxide in the atmosphere.

Biodiversity Is a Crucial Part of the Earth’s Natural Capital

Biological diversity, or biodiversity, is the diversity of the earth’s species, the genes they contain, the ecosystems in which they live, and the ecosystem processes of energy flow and nutrient cycling that sustain all life. Biodiversity is a vital renewable resource (Concept 3-4A) shows just two of the great variety of species found in tropical forests. Populations of these and countless other species in other ecosystems contain the variety of genes that make the genetic component of biodiversity. Genetic diversity provides a variety of genes that enable life on the earth to adapt to and survive dramatic environmental changes.

Ecosystem diversity-the earth’s variety of deserts, grasslands, forests, and mountains, oceans, lakes, rivers, and wetlands is another major component of biodiversity.

Each of these ecosystems is a storehouse of genetic and species diversity. In terrestrial ecosystems, soil is an essential component of biodiversity. Another important component of biodiversity is functional diversity-the variety of processes of matter cycling and energy flow within ecosystems and the biosphere.

Functional Diversity - The biological and chemical processes such as energy flow and matter recycling needed for the survival of species, communities, and ecosystems.

Ecological Diversity - The variety of terrestrial and aquatic ecosystems found in an area or on the earth.

Genetic Diversity - The variety of genetic material within a species or a population.

Species Diversity - The number and abundance of species present in different communities

Natural capital: the major components of the earth’s biodiversity-one of the earth’s most important renewable resources

Soil Is the Base of Life on Land

Most land is covered thinly by soil - a complex mixture of eroded rock, mineral nutrients, decaying organic matter, water, air, and billions of living organisms, most of them microscopic decomposers.

Soil formation begins when bedrock is slowly broken down into fragments and particles by physical, chemical, and biological processes.

Soil, the base of life on land, is a key component of the earth’s natural capital and biodiversity. It supplies most of the nutrients needed for plant growth, purifies, and stores water, and helps control the earth’s climate by removing carbon dioxide from the atmosphere and storing it as carbon compounds (Concept 3-4B).

Most mature soils-ones that have developed over a long period of time-contain at least three horizontal layers, or horizons, each with a distinct texture and composition that varies with different types of soils. Think of them as floors in the building of life underneath your feet.

The roots of most plants and the majority of a soil’s organic matter are concentrated in a soil’s two upper layers, the O horizon of leaf litter and the A horizon of topsoil.

In most mature soils, these two layers teem with bacteria, fungi, earthworms, and small insects all interacting in complex ways. Bacteria and other decomposer microorganisms found by the billions in every handful of topsoil break down some of its complex organic compounds into simpler inorganic compounds soluble in water. Soil moisture carrying these dissolved nutrients is drawn up by the roots of plants and transported through stems and into leaves as part of the earth’s chemical cycling processes.

The B horizon (subsoil) and the C horizon (parent material) contain most of a soil’s inorganic matter, mostly broken-down rock consisting of varying mixtures of sand, silt, clay, and gravel, much of it transported by water from the A horizon. The C horizon lies on a base of parent material, which is often bedrock.

The spaces, or pores, between the solid organic and inorganic particles in the upper and lower soil layers contain varying amounts of air (mostly nitrogen and oxygen gas) and water. Plant roots use the oxygen for cellular respiration. As long as the O and A horizons are anchored by vegetation, the soil layers as a whole act as a sponge, storing water and releasing it in a nourishing trickle.

Although topsoil is a renewable resource, it is renewed very slowly and thus can be depleted. Just 1 centimeter (0.4 inch) of topsoil can take hundreds of years to form, but it can be washed or blown away in a matter of weeks or months when we plow grassland or clear a forest and leave its topsoil unprotected.

Since the beginning of agriculture, human activities have accelerated natural soil erosion.

Critical Thinking

How does soil contribute to each of the four components of biodiversity?

The earth’s biodiversity is a vital part of the natural capital that helps keep us alive. It supplies us with food, wood, fibers, energy, and medicines-all of which represent hundreds of billions of dollars in the world economy each year. Biodiversity also helps preserve the quality of the air and water, maintain the fertility of soils, dispose of wastes, and control populations of pests.

In carrying out these ecological services that are part of the earth’s natural capital, biodiversity helps sustain life on the earth.


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