 All organisms use resources to maintain their existence and the use of these resources has an impact on the environment  Currently, the Earth is experiencing a population explosion  As populations increase, the demand for resources also increases

 As the number of reproducing adults increases, the rate of population growth increases rapidly  The population then experiences exponential growth, which is a pattern of growth in which the population grows faster as it increases in size  Despite this, there are factors that limit growth, such as the availability of food, water, or clean air.  These factors then cause the population to “level off”.

 The number that any given environment can hold is referred to as its carrying capacity.  When a population has not reached its carrying capacity, there are more births than deaths.  A population that is at the carrying capacity for its environment is said to be in equilibrium and will continue to fluctuate around its carrying capacity as long as there are natural resources available.

Each year in the United States alone, a typical person consumes resources equal to the renewable yield from approximately acres of forest and farmland!

 Modern societies, such as ours, require large amounts of land resources  Unfortunately, the extraction of these disturbs large areas of the Earth’s surface through surface mining and underground mining  As result, The Surface Mining Control and Reclamation Act of 1977 requires mining companies to restore the land to its original states and replant vegetation in a process of reclamation, which repairs much of the damage left by extraction.

 Growing populations increase the demand for food and when land is cleared for food production (agriculture), topsoil is lost through erosion and pesticides / insecticides interfere with life processes.  Topsoil is also lost through deforestation, the removal of forested land. › Negative impacts of deforestation (erosion by runoff) can be minimized through creation of retention buffers of trees along streambeds.  Development of land for urban development affects the environment in several ways: › Natural habitats are lost › Topsoil is eroded through construction › Agricultural land is lost › Runoff increases (asphalt coverage increases)

As people are becoming more aware of the need to protect the environment, most of the problems associated with land development are being solved: › Barriers are placed around construction sites to catch sediments from increase erosion › Wetlands are protected in the USA as they are recognized as valuable ecosystems › Landfills are now built to minimize the leakage of topic wastes › Bioremediation : (the use of organisms to clean up toxic wastes, are being used in contamination situations Plants that contain bacterial genes are grown in contaminated soils. The plants convert toxic compounds into non-toxic substances and then release them back into the air.

 Human activities cause more pollution, which can cause health problems › Humans have affected Earth’s atmosphere on a global scale › Acid rain, ozone depletion, and global warming are all caused by human activities

Smog is a photochemical haze caused by the action of solar radiation on an atmosphere polluted with hydrocarbons and nitrogen oxides. Smog in a city make air harmful to breath as the major chemical in smog is ozone.

 Humans require freshwater to live, in some areas the supply is too low to meet the demand.  Since 1960, freshwater use has nearly doubled and is expected to continue to increase.  Most people use freshwater in their homes for bathing, drinking, cooking and washing.  Crop irrigation also requires water, but much of it is wasted due to evaporation or it seeping into the ground before it can be used by the crops.

Pollution is another area where humans have an impact on water supplies. Water pollution sources are grouped into two main types: 1. Point Source 2. Nonpoint Source Ocean pollution is also possible in coastal areas due to untreated sewage being pumped through pipelines running along the ocean floor, extending far out into the ocean, creating “dead zones” of no living organisms

Point Source Nonpoint Source  Generates pollution from a single point of origin › Examples:  Sewage-treatment Plant  Industrial Site  Bacteria and viruses that enter water systems through improper disposal of sewage and toxic wastes, as result of illegal dumping, are common sources of point source  Generates pollution from a wide spread area › Examples:  Rainwater that absorbs air pollutants and becomes acidic  Runoff from road/parking lots that includes gasoline, oil, and other chemicals

Safe Drinking Water Act Ensures that everyone in the USA has access to safe drinking water Clean Water Act Ensures the elimination of discharge of pollutants into freshwater and restores water quality to levels allowing for recreational water usage.

Conservation of existing supplies is the best way to stretch the supply of freshwater because in many cases, new supplies of water are not readily available or may be too expensive to develop.