Describe how human activities are altering each of the nutrient cycles Solution The earth’s sustainability is very much dependent on the maintaining of its state of equilibrium. This state of equilibrium also determines the functioning of the ecosystem, which is restored through nutrient cycles. In recent years, there has been an increasing awareness that human activities have affected the earth sustainability in one way or another. Human activities that are known to be environmentally unfriendly, such as deforestation and fossil fuel burning, have directly and indirectly changed the biogeochemical and physical processes which affects the earth’s climate. Nutrient cycles always involve the achievement of equilibrium states, a balance in the cycling of the element between spheres. However, achieving these equilibrium states requires overall balance which usually involves elements being distributed on a global scale. Hence, a disruption in one cycle would result in the disruption in all other cycles. Below are some ways how human activities have contributed to the disruption of nutrient cycles. Use of Phosphorus fertilisers: The introduction and use of commercial synthetic fertilisers to boost plant growth are the main contributors to humans’ influences on the phosphorus cycle. As plants may not be able to utilise all of the phosphate fertiliser applied, which results in the phosphate fertilisers being transferred through the water run-off to water bodies in that area. This excessive run-off of phosphate eventually end up in streams or other water bodies which results in the changes of habitats and their equilibrium, and is eventually precipitated as sediments at the bottom of the water bodies. Other human sources of phosphate include the outflows from sewage treatment plants. Without the proper tertiary treatment which is expensive, the phosphate in the sewage would not be removed during various treatment operations, resulting in an extra amount of phosphate entering the water bodies and polluting them. As phosphate are released in small amounts in its accessible form in its original natural cycle, this extra phosphate released by human activities results in a change in the original phosphate cycle. This extra phosphate in water bodies are also a major contributor to the process of eutrophication, which causes excessive growth of water plants and algae populations. Usage of Fossil Fuels and Reduction of Carbon Sinks: Fossil fuels are one of the reservoirs for carbon in the carbon cycle. Mining of fossil fuels from the earth crust and using them to generate electricity especially since the industrial revolution has resulted in the release of carbon in the form of carbon dioxide into the atmosphere in large amounts. Further exacerbating the change in the carbon cycle, other human activities such as the clearing of vegetation, through deforestation or cutting of plants, results in lesser carbon sinks, further increasing the concentration of carbo.

1. Describe how human activities are altering each of the nutrient cycles
Solution
The earth’s sustainability is very much dependent on the maintaining of its state of equilibrium.
This state of equilibrium also determines the functioning of the ecosystem, which is restored
through nutrient cycles. In recent years, there has been an increasing awareness that human
activities have affected the earth sustainability in one way or another.
Human activities that are known to be environmentally unfriendly, such as deforestation and
fossil fuel burning, have directly and indirectly changed the biogeochemical and physical
processes which affects the earth’s climate.
Nutrient cycles always involve the achievement of equilibrium states, a balance in the cycling of
the element between spheres. However, achieving these equilibrium states requires overall
balance which usually involves elements being distributed on a global scale. Hence, a disruption
in one cycle would result in the disruption in all other cycles. Below are some ways how human
activities have contributed to the disruption of nutrient cycles.
Use of Phosphorus fertilisers:
The introduction and use of commercial synthetic fertilisers to boost plant growth are the main
contributors to humans’ influences on the phosphorus cycle. As plants may not be able to utilise
all of the phosphate fertiliser applied, which results in the phosphate fertilisers being transferred
through the water run-off to water bodies in that area. This excessive run-off of phosphate
eventually end up in streams or other water bodies which results in the changes of habitats and
their equilibrium, and is eventually precipitated as sediments at the bottom of the water bodies.
Other human sources of phosphate include the outflows from sewage treatment plants. Without
the proper tertiary treatment which is expensive, the phosphate in the sewage would not be
removed during various treatment operations, resulting in an extra amount of phosphate entering
the water bodies and polluting them.
As phosphate are released in small amounts in its accessible form in its original natural cycle,
this extra phosphate released by human activities results in a change in the original phosphate
cycle. This extra phosphate in water bodies are also a major contributor to the process of
eutrophication, which causes excessive growth of water plants and algae populations.
Usage of Fossil Fuels and Reduction of Carbon Sinks:
Fossil fuels are one of the reservoirs for carbon in the carbon cycle. Mining of fossil fuels from
the earth crust and using them to generate electricity especially since the industrial revolution has
resulted in the release of carbon in the form of carbon dioxide into the atmosphere in large

2. amounts.
Further exacerbating the change in the carbon cycle, other human activities such as the clearing
of vegetation, through deforestation or cutting of plants, results in lesser carbon sinks, further
increasing the concentration of carbon dioxide in the atmosphere. In addition, forest fire due to
deforestation or other causes, also results in the increase of carbon dioxide released. This
excessive release of carbon dioxide has led to carbon dioxide being one of the highest
greenhouse gases contributing to global warming and climate change nowadays.
Production of Sulphur dioxide:
Human activities, particularly our industrial activities, which involves the burning of coal and the
internal combustion engine results in the production of sulphur dioxide, causing an impact on the
sulphur cycle. Sulphur dioxide when released in their unnaturally excessive amounts can cause
several damage to the environment. Sulphur dioxide can precipitate onto surfaces where it can be
oxidised to sulphate in the soil, which is toxic to some plants. Sulphur dioxide can also be
reduced to sulphide in the atmosphere or be oxidised to sulphate in the atmosphere as sulphuric
acid, which is a principal component of acid rain. Acid rain, causes acidification of lakes and
streams and contributes to the damage of trees at high elevations and many sensitive forest soils,
in turn resulting to changes in certain components of other nutrient cycles as well.
Production of Nitrogen:
Extensive cultivation of legumes [For example, peanuts, soybeans, peas, beans etc], creation of
nitrogen fertilisers, pollution emitted by vehicles and industrial plants, are some ways of how
humans have increased the amount of nitrogen in biologically available forms.
Firstly, the application of nitrogen fertilisers to increase agricultural crop production has resulted
in the increased rates of denitrification and leaching of nitrate into groundwater. This excessive
amount of nitrogen entering the groundwater system would eventually flow into other water
bodies such as streams, rivers, lakes and estuaries, and can also lead to the process of
eutrophication, which causes excessive growth of water plants and algae populations.
Another agricultural practice which affects the nitrogen cycle includes livestock ranching. These
livestock release large amounts of the element nitrogen in the compound ammonia, into the
environment through their excretions. This nitrogen would then enter the soil system, before
entering the hydrologic system through leaching, groundwater flow, and runoff.
Other human activities such as fossil fuel combustion and forest burning to clear forest areas for
agricultural spaces also results in the increased deposition of nitrogen from atmospheric sources.
This then release nitrogen in a variety of solid forms through combustion. Sewage waste and
septic tank leaching are also examples of how humans and our activities contribute to this large
increase of nitrogen being released.
Vehicle Emissions:

3. Another contributor to pollutions would be our usage of vehicles. Vehicle usage and ownership
has been having a steep increase, and has now caused significant emissions that have negative
impacts to the environment. Vehicle emissions include the release of substances such as Mono-
nitrogen oxides (NO and NO2), Carbon monoxide and Carbon dioxide, and other hazardous air
pollutants. The extensive release of these substances affects the amount of the elements, such as
nitrogen and carbon, in the atmosphere and in turn affect and result in changes to their nutrient
cycles.