Human Impact on Biogeochemical Cycles Worksheet SCI/256

Human Impact on Biogeochemical Cycles Worksheet

Using the textbooks, the University Library or other resources, answer each of the following questions in 150- to 300-words.  Be sure to provide references for the sources you use.


Question Response

Your neighbor faithfully applies fertilizer to his lawn to ensure beautiful, healthy green grass.  Explain how your neighbor’s fertilizing habit affects at least one nutrient cycle.


Application of fertilizer on lawns may affect one or more of the nutrient cycles. The nitrogen cycle is one the nutrient cycles affected by application of the fertilizer (Hillel & Rosenzweig, 2011). The nitrogen cycle is a process through which exchanges of nitrogen occurs between living and non-living components of the planet. Plants require nitrogen during the growth process. However, plants cannot be able to use it in the form in which it naturally occurs. In the soil, bacteria convert nitrogen into a form that plants can use. As such, plant growth depends on the level of usable nitrogen in a particular area. In order to achieve robust plant growth, people add nitrogen fertilizers into the soil like in the case of my neighbor. Some of the nitrogen added is used by the plants while a large amount is washed into waterways during heavy rains. This nitrogen finds its way into rivers, streams, lakes, and other water bodies. This leads to eutrophication, which results to high growth of weeds and algae in the waterbodies. High growth of algae is linked to low oxygen levels in the waterbodies which impacts marine life.



Your friend commutes to work every day by driving a standard gasoline-powered car.  Explain how your friend’s commute affects one or more nutrient cycles


Commuting to work using a standard gasoline-powered car may have an impact on one or more of the nutrient cycles. A direct impact of using a gasoline-powered car is on the carbon cycle. Combustion of fossil fuels have largely increased the level of carbon dioxide in the atmosphere. Gasoline powered cars burn fossil fuels which release carbon dioxide and other gases into the atmosphere. It is estimated that burning fossil fuels produces about 7Gt of carbon annually (Benetar & Brock, 2011). Since the turn of the 18th century, the level of carbon dioxide in the atmosphere has significantly increased. The rate of increase is higher than the rate of carbon absorption by plants through the process of photosynthesis. The consequence of this is global warming which is characterized by an increase in the lower atmosphere’s average temperatures. Using a gasoline-powered car also releases nitrogen pollutants into the atmosphere, impacting the nitrogen cycle. During gasoline combustion, nitrogen dioxide and nitric oxide are released as by-products. These lead to formation of fog and acid rain when they mix with oxygen molecules and water vapor respectively.

Urban areas typically have lots of pavement and compacted soils.  Explain how these impermeable surfaces affect at least one aspect of the hydrologic cycle


Impermeable surfaces in urban areas impact a number of aspects in the hydrologic cycle. Water percolation into the ground is highly impacted by pavements and compacted soils found in urban areas. When precipitation occurs, water penetrates into the ground to form groundwater. The rate of percolation is highest in areas where there is dense vegetation cover such as forests (Benetar & Brock, 2011). In areas where soils are heavily compacted, there is high surface runoff. This is because the paving materials used are not porous and hence do not allow rainwater to seep into the ground. Urbanization alters the physical structure of the soil hence difficulties in water percolation. Another aspect that is highly impacted is evapotranspiration. In urbanized areas, there is little vegetation cover. Plants are important in moving water back into the atmosphere through evapotranspiration. When there are few plants, little water goes back to the atmosphere. As a result, most of it ends up in water bodies as runoff.


Environmental Issues



  • Benetar, S., & Brock, B. (2011). Global Health and Global Health Ethics. United Kingdom, UK: Cambridge University Press.
  • Hillel, D., & Rosenzweig, C. (2011). Handbook of climate change and       agroecosystems: Impacts, adaptation, and mitigation. London: Imperial           College Press.