Biosfera. Tabiiy resurslar, ulardan oqilona foydalanish va atmosfera muhofazasi. Suv

Water

Water is essential to life on Earth. It is a major ingredient of the fluid inside the cells of allorganisms. In fact, most organisms are 50 percent to 95 percent water. Respiration, digestion, photosynthesis, and many other important life processes can take place only in the presence of water. As Figure 2 shows, environments that have plenty of water usually support a greater diversity of and a larger number of organisms than environments that have little water.
Water Pollution Human activities can harm freshwater environments. Fertilizer-filled runoff from farms and lawns, as well as sewage dumped into the water, can lead to excessive growth of algae and plants in lakes and ponds. The growth and decay of these organisms reduces the oxygen level in the water, which makes it difficult for some organisms to survive. To prevent problems, sewage is treated before it is released. People
also are being educated about problems associated with polluting lakes and ponds. Fines and penalties are issued to people caught polluting waterways. These controls have led to the recovery of many freshwater ecosystems.

Water Pollution

Pollutants enter water, too. Air pollutants can drift into water or be washed out of the sky by rain.
Rain can wash land pollutants into waterways, as shown in Figure 16.Wastewater from factories
and sewage-treatment plants often is released into waterways. In the United States and many other countries, laws require that wastewater be treated to remove pollutants before it is released. But, in many parts of the world, wastewater treatment is not always possible. Pollution also enters water when people dump litter or waste materials into rivers, lakes, and oceans.
Surface Water Some water pollutants poison fish and other wildlife, and can be harmful to people who swim in or drink the water. For example, chemical pesticides sprayed on farmland can wash into lakes and streams. These chemicals can harm the
insects that fish, turtles, or frogs rely on for food. Shortages of food can lead to deaths among water- dwelling animals. Some pollutants, especially those containing mercury and other metals, can build up in the tissues of fish. Eating contaminated fish and shellfishcan transfer these metals to people, birds, and other animals. In some areas, people are advised not to eat fish or shellfish taken from polluted waterways. Algal blooms are another water pollution problem. Raw sewage and excess fertilizer contain large amounts of nitrogen. If they are washed into a lake or pond, they can cause the rapid growth of algae.
Ocean Water Rivers and streams eventually flow into oceans, bringing their pollutants along. Also, polluted water can enter the ocean in coastal
areas where factories, sewage-treatment plants, or shipping activities are located.
Oil spills are a well-known ocean pollution problem. About 4 billion kg of oil
are spilled into ocean waters every year. Much of that oil comes from ships that use ocean water to wash out their fuel tanks. Oil also can come from oil tanker wrecks, as shown in Figure 17.
¹Peter Rillero, Dinah ZikeEcology, 2005. (37, 78- bet)