The Critical Zone

Ecological Processes in the Critical Zone

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Desert Bighorn Sheep, Valley of Fire State Park, Nevada. How does a group of these sheep survive in the desert ecosystem and what impact do they exert on CZ processes?
Credit: Tim White, 2004.

The Earth's surface hosts a dynamic interplay of biotic and abiotic processes, all of which support the self-sustaining system that is the Critical Zone. The looming disaster associated with human activities and dominance of nature, however, threatens the balance of natural processes and challenges science to better understand the resilience of ecosystems and the CZ.


For this activity, I want you to complete the paper you have been working on for this lesson (see pages 3 and 5).


  1. To bring your newfound ecological knowledge fully to bear on Critical Zone issues, read the article entitled "Coupling between Biota and Earth Materials in the Critical Zone" by Ron Amundson and colleagues, which is available through Library Reserves.
    • As you read, be sure to think about the issues related to separating a direct biotic role in chemical weathering from climatic effects because of the strong influence of climate on biota.
    • Note the important role of plants in CZ processes: they pump essential elements and remove, temporarily store, and recycle them upon death; further, plants enhance weathering by altering CZ and river chemistry. Biota also mediates geomorphic processes by inhabiting, growing through and burrowing in soil, for example.
    • Leave this reading with an understanding of the concepts of the biomantle, or soil conveyor belt, and burrowing as a mediator between soil erosion and soil thickness.
  2. Complete your writing assignment begun on page 3 and continued on page 5 with any thoughts derived from this reading, specifically considering the site-specificity of burrow mediation and the soil conveyor concepts. We will return to issues regarding biosphere resilience and Critical Zone research in Lesson 12.
  3. Re-save your paper.

Submitting your work

Upload your paper to the "Lesson 10 - Ecological Processes " dropbox in Canvas (see the Modules tab) by the due date indicated on our Canvas calendar.

Grading Criteria

You will be graded on the quality of your writing. You should not simply write responses to the questions and submit them to me. Instead plan on writing a short stand-alone paragraph (or page or whatever you decide is necessary considering any constraints I might have placed on you) so that anyone can read what you've written and understood it. You should strive to be specific and complete in responding to the questions. Your answers should be analytic, thoughtful and insightful, and should provide an insightful connection between ideas. The writing should be tight and crisp with varied sentence structure and a serious, professional tone.