Section 3.3: The Nutrient Web

Outcomes

Students will:

  • Define the nutrient web and describe how it works.

  • Examine the various processes of the nutrient web, as well as the factors that influence the nutrient web.

Key Terms

Absorption / Bioavailability / Bioturbation / Decomposition / Desorption / Pedoturbation / Perturbation / Sedimentation

See content or Module Glossary for definitions

What is the Nutrient Web?

The nutrient web is the exchange of elements and minerals between living and nonliving things. Various physical, chemical, and biological processes help create nutrients, move the nutrients around, and change the bioavailability of the nutrients. All life on Earth depends on the nutrient web in some form or another.

How Does the Nutrient Web Work?

The nutrient web is an interconnected set of processes that happen in no particular order; in fact, these processes happen at the same time.

Formation

  • Parent materials form through the sedimentation of nutrients, such as minerals and elements, over a period of time and this leads to the formation of bedrock and the larger rocks in soil.

Perturbation

  • Perturbation covers all processes that alter soil and comes from the root word perturb, which means to alter from its original condition.

  • The break down and mixing of parent material and soil is called pedoturbation. Pedo refers to soil.

      • Everything from a landslide to plate tectonics is included in pedoturbation.

  • Bioturbation is the process when living creatures break down and mix the soil. The prefix bio refers to living creatures.

      • Bioturbation includes larger burrowing animals such as prairie dogs or moles, to smaller creatures such as worms eating their way through the soil.

Absorption

  • Nutrients released from the parent material can stay in the soil in either a solid state, in a liquid solution, or in a gaseous mixture.

  • The nutrients can be consumed or absorbed by plants and animals.

Desorption

  • The nutrients absorbed by plants and animals will eventually be released, or desorbed, through the exhaling of gases, expelling of solid and liquid waste, or upon the creature's death and decomposition.

Figure 16 shows the process of sedimentation, where heavier particles fall to the bottom faster than lighter particles.
Figure 16 shows the process of sedimentation, where heavier particles fall to the bottom faster than lighter particles.


Figure 17 shows the interconnectedness of the nutrient web. Original image by tom.
Figure 17 shows the interconnectedness of the nutrient web. Original image by tom.

What Factors Influence the Nutrient Web?

The nutrient cycle is affected by the same factors that influence soil formation from Section 3.1 and they are: parent material, climate, organisms, topography, groundwater, humans, and time.

Parent material refers to the rocks and sediments that are broken down to form soil.

  • The chemical composition of the parent material determines what nutrients are available in the nutrient cycle.

  • The physical structure of the parent material determines how easily it is weathered into soil. This affects how quickly the nutrient cycle can replenish the nutrients absorbed or lost (see Figure 18).

Climate refers to the long-term trend in weather.

  • Climate affects the rate of weathering and erosion of soil and parent material (Figure 19).

  • Erosion of parent material can add nutrients to the cycle, while erosion of the soil can remove nutrients from the cycle.

Any living plant, animal, fungi, insect, and microbe is referred to as an organism.

  • Organisms absorb and release nutrients, as well as help with the breakdown of parent material (Figure 20).

  • While the organism still has the nutrients within, it can transport the nutrients to new locations, making it easier or harder to access when released.

  • Organisms can also change the bioavailability of nutrients, making the nutrients easier or harder for other organisms to absorb.

Figure 18 shows an iron rich sedimentary rock. These are very weather resistant. Image by Andre Karwath.
Figure 18 shows an iron rich sedimentary rock. These are very weather resistant. Image by Andre Karwath.
Figure 19 shows a desert climate, where the soil is easily eroded away. Image by Luca Caluzzi.
Figure 19 shows a desert climate, where the soil is easily eroded away. Image by Luca Caluzzi.
Figure 20 shows prairie dogs emerging from their burrow. Image by Gunnar Ries.
Figure 20 shows prairie dogs emerging from their burrow. Image by Gunnar Ries.

The term topography refers to the slope, elevation, and orientation of the terrain (see Figure 21).

  • Having a higher elevation may limit access to key nutrients for plant and animal growth, hindering key steps in the cycle.

  • Having a large slope may cause a landslide, exposing new parent material, but washing away majority of the nutrients to the bottom of the hill.

Groundwater refers to the water stored within the ground.

  • Groundwater helps dissolve nutrients, making them easier to absorb by plants and animals.

  • Fast flowing groundwater can also wash away the nutrients, removing them from the local cycle as shown in Figure 22.

Figure 21 shows a landslide and exposed bedrock at the top of a mountain. Image by Sheri Terris.
Figure 21 shows a landslide and exposed bedrock at the top of a mountain. Image by Sheri Terris.
Figure 22 shows the flow of groundwater, which can erode the surrounding soil. Image by USGS.
Figure 22 shows the flow of groundwater, which can erode the surrounding soil. Image by USGS.
Figure 23 shows excavators mining for ammolite. Image by Hadal~commonswiki.
Figure 23 shows excavators mining for ammolite. Image by Hadal~commonswiki.

You may recall that when the term human is used, it refers to human activity that affects soil and parent material.

  • Industrial and agricultural activities, such as in Figure 23, alter soil chemistry through fertilizers or resource extraction, affecting what nutrients are available in the cycle.

  • Pollution in the air, water, and on the ground can add nutrients and toxins to the nutrients cycle.

Finally, time refers to the duration that the above factors have to act on the parent material and influence the nutrient cycle (see Figure 24).

  • Over long periods of time, a lot of parent material can be broken down to enter the nutrient cycle. Alternatively, a lot of nutrients can sediment out into parent material, making them unavailable for absorption.

  • As a whole, over long periods of time, there is a unique balance between all of the factors affecting the nutrient cycle.

Figure 24 shows the top of a mountain being weathered into smaller rocks. Image by Luis Paquito.
Figure 24 shows the top of a mountain being weathered into smaller rocks. Image by Luis Paquito.

A Dirty Crossword Lesson

Identify soil terminology from this section in a fun crossword. Lessons can be downloaded and adapted from here: https://bit.ly/3DdJggV

Additional Resources & References for Section 3.3

Resources

References

National Research Council of Canada. (1998). The Canadian system of soil classification (3rd ed.). Ottawa: Research Branch, Canada Dept. of Agriculture.

Soils of Canada. (n.d.). Welcome. Retrieved from https://www.soilsofcanada.ca/index.php