Section 7.3 How Human Activities Can Affect Sustainability

Eutrophication A process in which nutrient levels in aquatic ecosystems increase, leading to an increase in the populations of primary producers.

Greenhouse Gases Atmospheric gases that prevent heat from leaving the atmosphere, thus increasing the temperature of the atmosphere.

Greenhouse Effect The warming of Earth as a result of greenhouse gases, which trap some of the energy that would otherwise leave Earth.

Trophic Level A category of organisms that is defined by how the organism obtains energy.

Biomass The total mass of living organisms in a defined group or area.

Trophic Efficiency A measure of the amount of energy transferred from one trophic level to the next higher trophic level.

Bioaccumulation A process in which materials, especially toxins, are ingested by an organism at a rate greater than they are eliminated.

1. Identify the four systems of the Earth. The four systems of the Earth are the lithosphere, the hydrosphere, the atmosphere, and the biosphere.

Earth is considered a closed system. 2. Identify why and what types of matter are cycled through ecosystems. Matter such as carbon, nitrogen, phosphorous, sulfur, oxygen and water must continuously be cycled through ecosystems because no new matter is ever added to the planet and these types of matter are essential to life. Earth is considered a closed system.

3. What affect are human activities having on nutrient cycles? Human activities are affecting the balance of nutrients in ecosystems. There can be an increase or reduction in the amount of nutrients available and this may upset the balance among biotic and abiotic factors. This can compromise the sustainability of the ecosystem.

Nitrogen is used in fertilizers to enhance the growth of plants. 4. What happens to excess nitrogen from fertilizer that is not taken in by plants? Nitrogen is used in fertilizers to enhance the growth of plants. Often not all of the nitrogen is absorbed by plants and the excess is carried into aquatic ecosystems in the run off from rainfall. An increase in nitrogen in the water may cause an overgrowth of algae known as an algal bloom.

5. What affect does excess phosphorous have on bodies of water and how does it enter water ways? Phosphorous is also used in commercial fertilizers. If excess phosphorous ends up in lakes it has the same effect as nitrogen, eutrophication of the lake.

6. Outline the 6 steps in eutrophication. Fertilizer runs off from farmland into water. Algae bloom occurs. Submerged plants die due to reduced light. Algae and the other plants die. Bacteria use oxygen during decomposition. Oxygen levels in the water drop too low for fish to survive.

7. Identify some greenhouse gases that are being trapped in our atmosphere. Greenhouse gases being trapped in our atmosphere include water vapour, carbon dioxide and methane.

8. Fully explain how fossil fuels formed. Fossil fuels were formed millions of years ago. They are composed of the remains of plants that settled in places where a lack of oxygen prevented them from decomposing. Millions of years later the effects of pressure and heat turned the materials into what we now know as fossil fuels such as coal, petroleum and natural gas.

9. What is the link between the industrial revolution and the increased temperature of the Earth’s surface? The industrial revolution identifies a time in human history when humans began burning fossil fuels as a source of energy. This burning released large amounts of carbon dioxide that had been previously locked up under the Earth’s surface. This revolution marked the beginning of what is still massive amounts of carbon dioxide collecting in the atmosphere. This collection of greenhouse gases is the reason that there has been an increase in the Earth’s surface temperature.

10. Identify three efforts currently underway to try and reduce carbon dioxide emissions. Kyoto Protocol: an agreement signed by over 180 countries to reduce emissions. Protection of forests: Ontario and Quebec have protected roughly 50% of their boreal forests. Recycling: Nova Scotia has been leading the way in recycling by banning the disposal of many substances such as plastic beverage containers since 1996.

11. Why are trophic efficiencies usually quite inefficient? Trophic efficiencies are inefficient because only 10% of energy is passed from one trophic level to the next. This is due to the fact that most organisms use the majority of the biomass they consume for life functions and production of waste. Organisms also lose energy as heat.

12. What is biomagnification? Biomagnification is the increase in the concentration of toxins in the body tissues of organisms as it moves from one trophic level to the next. In other words, the top consumer in a food chain will have a much higher level of a toxin in their tissues than a primary consumer.

13. What is DDT and PCB’s and why are they banned substances in North America? DDT is an agricultural insecticide. PCB’s are a compound previously used by industries and could be found in plastics, paints, rubber compounds and many other applications. Both of these substances are toxic to organisms and have subsequently been banned in North America.

14. Using the beluga whale as an example, explain how all terrestrial and aquatic ecosystems on the Earth are connected. We must begin to understand that all ecosystems are connected. Chemicals we use on land can reach aquatic ecosystems and have widespread effects. Scientists have been studying beluga whales in the St. Lawrence river and have found dozens of chemicals that have bioaccumulated in their tissues and subsequently they have some of the highest cancer rates of any wild animal studied. The pollutants from run off have accumulated in the sediment of the river where they were consumed by krill and worms, who were consumed by the beluga whales.