How do our activities affect the environment?

Introduction of any substance or related activity which can adversely affects the physical, chemical or biological properties of the environment or causing any harmful effect to the environment ultimately leads to the degradation of the ecosystem as a whole.
Human beings are an important part of the environment but through their activities directly or indirectly they are contributed to pollute the environment. The major environmental pollution are : Air pollution, water pollution, noise pollution and soil pollution.
The growing need of vehicles mainly in metro cities contributes to air pollution, vehicles produce high levels of pollutants like carbon monoxide, carbon dioxide, nitrogen oxides and smoke.
Many industries are also responsible for causing air pollution. Petroleum refineries are a major source of gaseous pollutants like sulphur dioxide and nitrogen dioxide.
Industries discharging harmful chemicals into rivers and streams caused pollution of water. Untreated sewage thrown directly into rivers is one of the major contributor to water pollution as the contaminated water contains harmful microorganism which can cause diseases like typhoid, jaundice and cholera.
Introducing harmful chemicals or substances directly or indirectly to contaminate the soil is soil pollution. Human activities such as dumping, accidental leaks and spills and manufacturing process effects soil's health.
The unwanted or excessive noise that cause harmful effects or disturbs the balance of animals or humans life is noise pollution. Outdoor noise caused by transportation system such as vehicles, trains etc. The continuos blowing of horns for no reason also causes noise pollution. Indoor includes building construction, through the use of large machines, music performances where loud speakers were used etc. are referred as irritants.

Humans are a part of the natural environment. Unfortunately, we have not yet learnt to moderate our activities in such a way as to help the environment. Human activities often lead to degradation of the environment.
Impact of humans include:

pollution - land, freshwater creeks and rivers, seas and oceans, and air
deforestation and destruction of habitats
endangerment and extinction of flora and fauna species
introduction of invasive and parasitic fauna and flora species to new areas
increased desertification of land - this often occurs because, when humans try to increase fertile land in one area, they must divert needed resources from another area
altering natural waterways which can increase the risk of flooding
Interfering with the natural fire cycles of an area (one cause of increased bushfire problems in Australia)
overuse of natural resources, resulting in depletion of some of these resources
climate change and the development of extreme weather conditions: scientists continue to debate how much humans actually contribute to climate change and/or global warming, but there is evidence that our activities do contribute in some part
rising sea levels
increased erosion of land as a result of mining or agricultural activities
mining activities not only can destroy the vegetation of the area, but can contribute to instability in the earth's crust.

There can be some neutral impacts. Native people in many lands lived in harmony with their environment for thousands of years. The native Americans and Australian Aborigines, for example, used only what they needed, and did not pollute their environment or alter it negatively and permanently.

Fortunately, man is learning (a little too late) that there are activities he can undertake to improve land he has already degraded. This may involve:

conservation, monitoring of and captive breeding programmes for endangered species
restoring degraded ecosystems by planting trees specifically native to the area, and removing introduced species
removal of pollutant materials

Overhunting

When humans over-hunt key predators such as lions, tigers and bears, they remove the very animals that keep plant consumers in balance and prevent overgrazing. A healthy ecosystem has a balance of predators and prey that naturally cycle through life and death sequences. Over-hunting often results in ecosystem species imbalance and environmental stress. Humans also practice commercial overfishing, where massive fishing nets result in “bycatch,” in which unwanted fish are caught in nets and then thrown away. Bycatch results in the death of one million sharks annually. Large weights and heavy metal rollers that are used with the commercial fishing nets also drag along the bottom of the ocean, destroying anything in their path including fragile coral reefs.

Deforestation

Humans have always cut down trees throughout history. However, they now have the resources of multimillion-dollar equipment that drastically increases the rate of tree removal. The world’s rainforests are being destroyed at a rate of 78 million acres per year, resulting in vegetation degradation, nutrient imbalance, flooding and animal displacement. Trees also act as a natural air filter in the carbon cycle by taking in carbon dioxide and releasing oxygen, so deforestation contributes to global warming. Some estimates indicate that canopy forest species will be reduced by 35 percent by 2040 if deforestation continues at the same rate.

Pollution

Vehicles, trains and planes emit toxic gases that include carcinogenic particles and irritants, creating air pollution. Humans have also dumped large amounts of pesticides, such as organophosphates, onto crops that migrate into groundwater and bodies of water, poisoning ecosystems. Plants and animals die from exposure to pollutants such as excess nutrients from chemical fertilizers and other harmful chemicals. Pollution is increasing around the world and results in loss of biodiversity causing severe damage to self-sustaining ecosystems.

Land Conversion

Through urban development, the continued rapid construction of road systems and buildings has changed the Earth's natural surface, removing soil nutrients, surface vegetation and trees that filter the air and equalize the carbon cycle. Urbanization also displaces animals and increases environmental pollution from vehicles and factories. A system of highways also causes serious migratory obstacles for animals and replaces native plants with impermeable concrete, resulting in habitat destruction. Since the concrete is impermeable, it doesn’t allow water to seep through, resulting in increased vulnerability to flooding. This practice of human construction continues at a rapid pace, leading to urban sprawl, where cities are essentially forever expanding outside the traditional inner-city limits.