12.1 The “waste” generated by economic systems does not occur in ecosystems

360

12.1–12.2 Science

image
(USFWS photo by Susan White)

image

How do modern garbage heaps differ from those left by ancient people, such as that at Emeryville?

Just north of Oakland, California, lies the Emeryville Shellmound, a pile of discarded clam, mussel, and oyster shells that was once over 60 feet high and 350 feet wide. These are the remnants of more than 2,000 years of habitation by Native Americans. Around the world, it was common to toss out waste in open dumps, and everywhere that humans lived, their trash accumulated. However, as the human population grew and the intensity of economic activity increased, we littered Earth with more diverse types of waste, including toxic waste. In some places, where open dumps are still in use, waste deposits have reached the size of small mountains (Figure 12.1). These growing accumulations on land and sea loom as one of the great environmental challenges. By understanding the way natural ecosystems generate and recycle their own waste, we can find models for how societies might address this challenge.

A MOUNTAIN OF WASTE
image
FIGURE 12.1 The amount of waste generated by the billions of humans living today is astounding. Solid waste from cities, called municipal solid waste, is especially apparent because vast quantities can accumulate in waste dumps. In several developing countries, waste dumps attract many people searching for usable resources.
(Jefri Tarigan/Anadolu Agency/Getty Images)

In the early days of human societies, it didn’t matter much if people just tossed waste out their back windows. They produced little of it and their settlements were small. Critically, most of the waste consisted of natural materials—which simply decomposed over time due to the activities of scavenging animals, plants, and microorganisms. The chemical elements contained in those wastes were eventually recycled by the ecosystem. If one patch of land became too polluted, communities could always just pick up and move.

With explosive human population growth and development of the modern industrial society, however, the quantity, types, and sources of wastes produced by humans have changed radically (Figure 12.2). Today, much of human waste no longer cycles freely and rapidly but too often meets a dead end—buried in a landfill where it cannot be decomposed easily, preventing the elements it contains from re-entering the biosphere. Many human-made chemicals, such as plastics, have no natural cycling pathway, or are manufactured in such abundance that those pathways cannot degrade them quickly enough.

SOURCES OF WASTE
image
FIGURE 12.2 Nearly every human activity results in the production of some type of waste. In modern urban environments, the numerous sources of waste range from individual residences to factories, power plants, commercial enterprises (e.g., stores and hotels), as well as institutions such as schools, hospitals, and nursing homes.

361

A first step toward efficiently recycling human-generated waste is to understand the cycling of materials in nature. The law of conservation of matter (see Chapter 2, page 42) states that matter in a closed system cannot be created or destroyed, only changed in form. As a result, the chemical elements of which all matter is composed can cycle indefinitely in ecosystems. For example, the carbon, nitrogen, phosphorus, and sulfur cycles (described in Chapter 2, Chapter 7, Chapter 8, and Chapter 13) trace the movement of these elements through ecosystems. Similar cycling occurs for all the other elements, like calcium and iron, found in living things.

Every living organism can be reduced to its building blocks, making them available for other organisms. Every resource made by nature returns to nature—decomposed by microbes, plants, and animals. Even crude oil will degrade under the right conditions. And, at the very largest scale, the Earth system recycles the minerals that make up rocks, the most basic geologic component of the planet (see Appendix B).

Think About It

  1. What is the eventual fate of elements found within dead plants, animal waste, and other matter?

  2. Earth is a closed system to nearly all forms of matter. How, then, has the biosphere been able to support countless life forms across millions of years?

  3. What basic steps might be taken to make our wastes better able to enter Earth’s natural cycles? (Hint: Consider the carbon cycle in Figure 2.13, page 43, as a model.)