Human Influences on the Environment

The rapid expansion of the human population has had a huge and devastating impact on the environment. Cutting down trees to make room for housing and farmland has destroyed habitats and increased carbon dioxide levels by reducing the number of trees which absorb carbon dioxide for photosynthesis. Burning fossil fuels has added to the increased carbon dioxide, causing the average temperature on Earth to steadily increase.

Air pollution

Burning fossil fuels releases sulfur dioxide and carbon monoxide which result in air pollution. Sulfur isn’t present in the fuels themselves but impurities in fuel contain sulfur which form sulfur oxides when burned. Carbon monoxide is formed when fuels are burned in a limited supply of oxygen.

Sulfur dioxide reacts with water vapour in the atmosphere making rain more acidic. Acid rain has the following adverse effects in our environment:

• reduces the pH of ponds and rivers, making it difficult for aquatic life to survive

• damages the waxy coating on leaves, reducing photosynthesis

• reacts with minerals in the soils, limiting the availability of nutrients to plants

• corrosive effect on limestone and marble buildings or statues

Carbon monoxide is released when fuels are burnt in limited oxygen. It binds to the haemoglobin in red blood cells instead of oxygen, reducing the amount of oxygen delivered to cells for respiration. This causes the heart to beat more vigorously, resulting in increased blood pressure and an increased risk of a heart attack.

Human activities have caused a significant increase in the levels of greenhouse gases in our atmosphere. Large scale deforestation to make room for housing and agriculture means less carbon dioxide is absorbed by trees for photosynthesis. Burning fossil fuels to generate electricity or to power cars also increases the level of carbon dioxide, nitrogen oxides and water vapour in the atmosphere.

Global Warming

Infrared radiation (heat) is emitted from the Sun towards the Earth’s surface. Some of this heat is absorbed but some is reflected back out towards space. Greenhouse gases in the atmosphere can trap some of this reflected infrared radiation, causing the Earth to become gradually warmer. A warming planet will cause the polar ice caps to melt, resulting in flooding and destruction of habitats which could have a destructive effect on many species and the rest of the food chain which depend on them. Global warming will also result in extreme weather events such as droughts, cyclones and hurricanes.

Water pollution

Water can become polluted by human sewage, excessive use of fertilisers and pesticides and the formation of acid rain from burning fossil fuels.

What we flush down our toilet might be disgusting to you, but its fine dining for a group of bacteria. Human sewage dumped into water causes an increase in growth of the bacteria which feed on faeces. The respiring bacteria use up all of the oxygen in the water, making it difficult for anything else to survive. In sewage treatment plants, plenty of oxygen is added to the sewage to encourage bacteria to fully breakdown the waste before it is discharged into the sea or rivers.

Certain invertebrate species cannot survive in polluted water so an analysis of the different aquatic invertebrates in a body of water can indicate the extent of pollution. For example, stonefly nymph and mayfly larvae cannot tolerate even small levels of pollution so the presence of these species means that the water is not contaminated. Species such as these which provide information about levels of pollution are called indicator species.

Eutrophication

Fertilisers are used by farmers to add nitrate to the soil, which are taken up by plants to make proteins for increased growth. The problem is that the nitrates are extremely soluble and are easily washed away from soil when it rains in a process called leaching. The rain containing dissolved nitrates makes its way into ponds and rivers where they are absorbed by algae causing a huge increase in algal growth. The algae can divide so rapidly that they completely cover the surface of the pond (known as algal bloom), blocking sunlight to plants growing at the bottom of the pond. The plants die because they are unable to photosynthesise and are decomposed by bacteria. The increasing bacterial population use up all of the available oxygen through aerobic respiration, reducing the amount of oxygen available for other aquatic organisms which struggle to survive in oxygen-depleted water.

Deforestation

At the current rate of deforestation, the world’s rainforest could completely vanish within a hundred years. Humans are removing trees from rainforests for a number of reasons:

• to make room for housing and agriculture

• to use the wood for fuel, paper or furniture

Deforestation is a problem because it results in the loss of habitats, threatening the existence of certain animal populations and the rest of the food chain. Since trees absorb carbon dioxide and release oxygen during photosynthesis, the removal of trees increases carbon dioxide and reduces oxygen in our atmosphere. Trees also hold soil in place so deforestation produces looser soil which is less able to retain minerals and water. Water and minerals are easily leached (washed away) from the soil.

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