2.Human exploitation of natural resources has modified the environment.Give examples of renewable and non-renewable resources.What are the appropriate attitudes and practice in the wise use of our natural resources(e.g. timber and fish).

Natural resources refer to all materials in nature that are required by humans for their well-beings.Over-exploitation of natural resources refers to the over-use of natural resources,which may eventually lead to their exhaustion.Human exploitation of natural resources has modified the environment.The improper use of natural resources and improper management of technology during exploitation may lead to adverse effects on the environment.In addition,the over-exploitation of natural resources and environment problems today are cloasely related to the increase in world population.Natural resources are customarily classified into renewable resources and non-renewable resources.

Renewable resources

Renewable resources are resources that can be regenerated fairly rapidly through natural processes.Examples include oxygen,minerals in soil,wildlife,timber,fish,and fresh water.Theoretically,these resources are renewed naturally and are always available.However,if the rates of use exceed the rates of renewal,the resources will become depleted.Thus,the proper management of renewable resources becomes an important topic in environmental science.Three of the renewable resources:timber,fish and fresh water,will be discussed below.

Timber

Timber is a very useful raw material in our daily lives.We obtain timber by removing forests in various parts of the world.Humans depend very much on timber for their well-being.The wood consumed by humans can be divided into industrial wood and fuel wood.Industrially,people make use of timber for construction,making furniture,and manufacturing of paper for education and communication purposes.In terms of fuel,a significant portion of the world population is still dependent on timber as the principal source of energy for heating and cooking.

Over-exploitation of timber can pose serious threats to the environment and,in turn,to human in different ways:

-Destruction of habitats

-Loss of nutrient availability

-Soil erosion and its consequences

-Climatic changes

Fish

Water covers about 70% of the surface of the Earth.This huge biological system comprises very diverse habitats and very great biodiversity.The oceans are very important for human existence.It is a regulator of atmospheric composition and a site for nutrient cycling.The oceans,of course,are important in supplying humans with food;the most important in supplying humans with food;the most important ones are fish.

The earliest use of the oceans by humans was probably for food.People living along the oceans captured fishes and other organisms for consumption.Fishes are an important element of the human food supply.They account for roughly one-fifth of all animal proteins in human diet.Aroung a billion people in the world rely on fishes as their primary source of proteins.Marine fishing is an important human activity.It supports the living of about 200 million employees in related industries globally.

In the past,people caught fish by using some primitive fishing technologies.These practice only damaged the aquatic environment to a little exent.However,there were changes in the second half of the 20th century.The development of new technologies and fishing methods has enabled humans to permeate more and more parts of the oceans.Today,the intensive exploitation of fish has become a general concern.The decline of fish stocks in various parts of the world has beed reported.If fishing activities are not under control,this valuable resource will be depleted eventually.The intensive exploitation of fish also results in great impacts on both the environment and the ecosystems.

-Impact on the environment

The modern fishing methods involve large and power ful vessels,effective nets and traps,as well as advanced electronic devices.These usually lead to destruction of aquation habitats in fishing areas.Dredges and bottom trawls are responsible for the damages.In trawling,heavy nets are dragged along the ocean floor.This damages sea grass,disrupts the availability of food for aquatic organisms,and kills a large number of bottom-dwelling organisms,especially coral reef and the fishes associated.

-Impact on the ecosystem

The intensive exploitation of target fish stocks can cause a great impact on the ecosystem.The food web will be affected by the removal of a large biomass of organisms at a critical trophic level.This may lead to an uncontrolled increase in particular type(s) of organisms occupying the lower trophic levels due to the lack of predators;this may also push other type(s) of organisms occupying the higher trophic levels to extinction due to the lack of food.

Futher,significant portions of the fish caught from the sea are non-target species.They include species such as whales and sea turtles that are not in demand,inferior in quality,or beyond the fishing quotes.The non-target species are not sold in the market,but are mostly thrown back to the sea in the form of dead bodies.This greatly threatens the aquatic biodiversity.

Fresh Water

Water is abundant on the Earth,most of it is unavailable for human use due to salinity or unreliability.Only less than 3% of water on the Earth is fresh water,and about three-quarters of which is tied up in glaciers ,ice caps,and snowfields.Nevertheless,ground water is another important source of fresh water.It is held underground in porous,waterbearing layers of sand,gravel and rocks.

In the global scale,agriculture accounts for most of the water used by humans.Humans use a large quantity of water in agriculture,especially in developing countries.Industry accounts for about 1/4 of the water used by human.The cooling water used in power stations is by far the largest single industrial use of water.Primary metal smelting and fabrication,petroleum refining,pulp and paper manufacturing,and food processing altogether account for about 2/3 of the water used in industry.Only a small fraction of water is consumed domestically for cooking,bathing and cleaning household utilities.

Gound water plays an important role in providing fresh water for agriculture and domestic uses,especially in rural areas.Over-use of the ground water causes the following problems.

-Water depletion

-Subsidence

-Sea water infiltration

Non-renewable resources

Non-renewable resources are resources that are limited in availability.They are fixed in total quantity in the Earth's crust and are not replenished by natural processes in short time scales.Notable examples include fossil fuels(petroleum,coal and natural gas)and minerals(including different types of metallic and non-metallic resources).They are essential for humans for various purposes.If these materials continue to be extracted rapidly,their exhaustion will be speeded up.Thus wise utilization of non-renewable resources and the adoption of substitutions of these resources are essential.

Fossil Fuels

Fossil fuels include petroleum,coal and natural gas.They are formed from the fossilized remains of prehistoric organisms.The processes of formation take millions of years and thus fossil fuels are regarded as non-renewable resources.

Fossil fuels are the major source of energy used by humans.A substanial quantity of fossil fuels is used to produce electricity.Electrical energy,a convenient form of energy,is thus available for various purposes,such as operating machinery,heating,cooking,lighting and also transportation.

Today,people are concerning about the total reserves of fossil fuels on the Earth.They are also concerned about the impact of the extensive utilization of fossil fuels on the environment in the following aspects:

-Generation of various air pollutants

-Accidental contamination of the environment