model 4—the phosphorus cycle - chsapbiology.com€¦ · web viewof phosphorus. pools are areas...

Model 4—The Phosphorus Cycle

1. Describe how phosphates are able to move from the aquatic environment to the terrestrial environment.

2. Why do organisms need phosphates?

3. Compare this biogeochemical cycle to the others you have examined and describe the one significant feature that makes this cycle different.

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4. Describe how rock is weathered.

5. Describe how rock uplift might occur.

6. Terrestrial plants get their phosphates from ______________. Terrestrial animals get their phosphates from ___________.

7. Describe the role of detritovores in the model shown above.

8. How do phosphates become part of rock?

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Model 5—Global Phosphate FluxThe Diagram below shows how phosphorus cycles globally and includes overall quantities of phosphorus. TgP stands for Teragrams of phosphorus. Pools are areas in which phosphorus resides and fluxes describe the movement of phosphorus from one place to another. Eutrophication is the process by which aquatic plants (mostly phytoplankton) use excessive nutrients from water to grow and reproduce. As the plant population increases, the quantity of plants dying increases. Dying plants are broken down by aerobic bacteria which use up much of the oxygen in the water causing the death of many organisms. The number of years shown in the boxes indicate the residence time of phosphorus in that location (it tells you how long phosphorus remains in that location).

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Schematic Diagram of Main Parts of Global Phosphorus Cycle. Pools are in TgP, fluxes in TgP/yr, and turnover times are in years. The grey arrows are the fluxes that are entirely or partly anthropogenic. P is building up in terrestrial soils as a result of P fertilizers, and is leaking into rivers, lakes, and coastal waters, where it is the main driver of

1. Use the data in the diagram to identify the residence time of phosphorus for each of the following locations:

a. Ocean sediment____________b. Plankton and fish______________c. Surface Ocean Water____________d. Soil________________e. Plants__________________f. Dust_________________

2. There is not a residence time listed for animals in this diagram. Why do you suppose there is no value shown here?

3. Which location has the longest residence time? ________________ Given this information, what problem could this cause for terrestrial organisms?

4. What does anthropogenic mean?

5. Using the information given to you above, why do you think humans need to use fertilizers that contain phosphorus (i.e. why isn’t there enough in the soil without fertilizers).

6. How do humans get phosphorus to use it as fertilizer or in industry?

7. If the mined phosphorus was removed from the model, what would be the effect of the amount of phosphorus in the soil?

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8. If you only consider the part of the diagram shown below, why might phosphorus be a limiting nutrient for many ecosystems?

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Model 6—Sulfur Cycle

Fig. 3 Simplified marine organic sulfur cycle.

Schematic overview of organic sulfur reservoirs and fluxes. All numbers refer to organic sulfur, except for the oceanic sulfate inventory and the land-atmosphere flux (total S). Known and calculated organic sulfur fluxes are shown as solid lines and unknown fluxes as dotted lines. The red circle indicates the rapid and important cycling of labile DOS compounds such as DMSP (depicted in the small white box). For corresponding data and references, see table S3.

1. Why do living organisms need sulfur?

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2. According to the model, how does sulfur move from the terrestrial environment to the aquatic environment?

3. According to the model, how does sulfur enter the atmosphere?

4. In many areas of the world, marine primary productivity has decreased as a result of increased absorption of carbon dioxide. This occurs because increased CO2 absorption causes a decrease in the pH of the water which might not be optimal for many populations of phytoplankton to survive and reproduce. Using data from the model, predict the effect of continued ocean acidification on the cycling of sulfur in marine environments. Justify your answer.

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Extension Questions

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Scientists are debating what effects global climate change may have on nutrient cycles. As soil becomes warmer, especially at far northern latitudes, nutrients in the soil should become more available to plants, stimulating plant growth. One hypothesis is that more carbon will end up stored in the soil as a result, because plants will pull carbon from the atmosphere and transfer it to the soil reservoir as they shed leaves or die. Under this hypothesis, increased flux of carbon from the atmosphere to the soil would act as negative feedback counteracting climate warming because less carbon in the atmosphere would lead to less warming. To test whether the carbon flux actually changes in this way when nutrients are made more available in a tundra ecosystem, researchers are conducting a long term study in Alaska. For 20 years, they have added fertilizer to treatment plots while leaving control plots unfertilized. Recently, they estimated amounts of carbon by measuring biomass above ground and below ground in both sets of plots. Aboveground biomass consists of living plant material, whereas below ground biomass consists mostly of nonliving organic material stored in the soil and not yet decomposed. Some of the research teams results are presented in the graph below.

1. Calculate the sizes of aboveground, belowground and total carbon pools (in g C/m2) for the control and fertilized treatment groups. Clearly show all of your work.

2. What do the aboveground data indicate about the effect of fertilizer on plant growth?

3. What do the belowground data indicate about the effect of fertilizer on organic material stored in the soil?

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4. Do the data support the hypothesis that the net effect of increased nutrient availability will be to remove carbon from the atmosphere and store it in the soil? Justify your answer.

5. Use what you know about biogeochemical cycles and suggest an alternative hypothesis that might better explain the data.

6. Based on this data, would you predict that the warming of tundra soil will decrease the atmospheric concentration of CO2 and act as a negative feedback to climate change, or increase it and act as positive feedback? Justify your answer.

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