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Unit 5: Agriculture and Freshwater Pollution

Chris Sinton, Ithaca College

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Initial Publication Date: March 2, 2017 | Reviewed: December 10, 2020


Units 3 and 4 of this module explored how water resources are used for agriculture in the United States and how this can vary depending on location. In Unit 5, students explore how agricultural practices can affect the water quality in streams, rivers, lakes, and coastal areas. Important concepts in this unit include processes that transport suspended material (e.g., sediment) and dissolved material (e.g., nutrients) away from crop fields and into regional water bodies. The effects of dissolved nutrients on the health of the water ecosystems will be presented with examples of hypoxic zones in coastal areas and lake eutrophication. This last unit is well-suited to foster student advancement in systems thinking.

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Learning Goals

Unit 5 is designed to help students advance in achievement of Module Learning Goals 1, 3, and 4:

  • Module Learning Goal 1: Explain how freshwater availability and management practices pose threats to ecosystem integrity, human well-being, security, and agricultural production.
  • Module Learning Goal 3: Explain what controls geographic variability in irrigation, groundwater mining, and ecosystem impacts of agriculture in the United States.
  • Module Learning Goal 4: Apply geoscience information and methods in interdisciplinary assessments of the sustainability of water systems.

The unit also has the following more specific learning objectives.

Upon completion of the unit, students should be able to:

  1. Articulate how agricultural practices can lead to impairment of water quality and aquatic ecosystem integrity.
  2. Construct a conceptual model that depicts the influences of agricultural practices on the eutrophication process and incorporates key components of systems thinking.

Context for Use

This unit has been designed as the last in the module Water, Agriculture, and Sustainability. It can also be incorporated into an introductory-level earth or environmental science course as a two-day stand-alone activity. If incorporating it as a stand-alone unit, students should have a working knowledge of the hydrologic cycle and basic agricultural practices (e.g., tilling, irrigation, fertilizer use).

Class Size: This can be adapted for a variety of class sizes.

Class Format: The activities in this unit are suitable for a lecture or lab setting but may not work as well as a homework assignment. If done in class, students should work in groups.

Time Required: Each of the two lessons in this unit can be completed in a 50-60 minute class period.

Special Equipment: None

Skills or concepts that students should have already mastered before encountering the activity: Before the lessons, students should complete a reading assignment (see below) in order to understand basic concepts about non-point source pollution and agriculture.

Description and Teaching Materials

Unit 5.1 - Agriculture as a Source of Water Pollution (60 minutes)

The objective of Unit 5.1 is to foster student understanding of the concepts of Non-Point Source (NPS) pollution and the process of nutrients and sediments moving from agricultural operations into water bodies.

To prepare students for the class, the instructor can direct them to one or more of the following readings:

There are four parts to the lesson:

  • (10 minutes) Mini-lecture on Agricultural Non-Point Source Pollution: The instructor should give a mini-lecture that covers the basic concepts - the following PowerPoint file may be used: Ag and Pollution Intro (PowerPoint 2007 (.pptx) 73kB Jan23 17). Use only the first page to display the concepts and check for comprehension of the reading. The idea is to convey the processes that move material from the agricultural site (field or animal feedlot) into water.
  • (10 minutes) Brainstorming on Agricultural Activities: The instructor can show the diagram on the first slide of the above PowerPoint on a screen in the classroom. Divide the class into groups of four or five (self-selected) and ask each group to create a list of agricultural activities that can lead to the introduction of suspended and dissolved material into groundwater and surface water. Students should have gained an understanding of this from the reading. Each specific activity should have a description. When time is up, have the groups share their findings with the rest of the class. The instructor can create a master list on the chalk/whiteboard or use the suggested list on the second slide of the PowerPoint file.
  • (20 minutes) Components of Non-Point Source Pollution and Nutrient Runoff: Keeping students in their groups, have them discuss what are the components of NPS that are of concern. Have each group come up with a list of these components and differentiate between suspended and dissolved. Each component should have a definition and an example.
  • (10 minutes) Wrap up: Instructor summarizes the components that are of concern in NPS pollution (this is on page 5 of the Powerpoint file) and introduces the concept of eutrophication due to increased nutrient levels in surface water (page 6). This will prepare students for Lesson 2.

Unit 5.2 - Thinking in Systems: Modeling the Impact of Agriculture on the Eutrophication Process and the Development of Dead Zones (60 minutes)

One of the major effects of agricultural non-point source pollution is eutrophication of water bodies due to nutrient runoff. Rivers draining regions that are intensively cultivated can carry excess nutrients into coastal areas. The following image is a schematic of this process:

Hard copies of this can be handed out to students. The instructor can use a whiteboard/chalkboard to write a summary of impacts. Here is a list taken from NSTC (2003): Unit 5 Instructor notes (Acrobat (PDF) 41kB Jun5 15)

Eutrophication of coastal areas linked to excess nutrient input from rivers that drain agricultural regions has led to hypoxic regions or "dead zones." After students have studied the processes of eutrophication, the instructor should then divide the students into groups and assign each group a case study. The Committee on Environment and Natural Resources (2010) report (see below in the reference section) has eight short case studies in the US in Appendix II. As an alternative, case studies can be assigned as readings in advance of the class. Groups will read, discuss, and report out to the rest of the class on what can be learned from their case study. Working with case studies gives students the opportunity to direct their own learning as they explore the science underlying the complexity of coastal eutrophication. Guidance on getting the most out of case studies can be found here: Using Investigative Cases module.

After each group reports, the instructor should lead a discussion that compares and contrasts the different case studies and highlights the links to agricultural activities. This should culminate in the generation of a conceptual box model depicting the influence of agricultural practices on the processes and outcomes of the eutrophication process. Working through this process - essentially teasing apart elements seen in the schematic above - will prepare students for the success in completing the formative assessment provided below. It also provides the perfect opportunity to incorporate many of the elements and concepts of systems thinking. Instructors are encouraged to use language like reservoirs, fluxes, feedbacks, non-linear change, dependent variables, and independent variables in describing the inputs, processes, and outcomes displayed in the conceptual model. What follows are three resources that can help you think through how you want to use the case study analysis and concept map building activity to enhance understanding of complex system dynamics and advance systems thinking in your students.

Teaching Notes and Tips

After students complete Lesson 1, you may want to show a set of images showing examples of tilling a field, topsoil erosion, and sediment in a river.

Lesson 2 can be varied in terms of the chemistry concepts. If the students are predominantly science majors with a background in chemistry, the instructor can explore aqueous chemistry in more depth.

Click on the links included in Unit 5.2 for additional guidance on getting the most out of case studies and in fostering systems thinking.


Formative Assessment

A formative assessment of the unit goals can be completed using the attached

and associated .

Post-Module Assessment

At this point, students will have completed all five units of this module and are ready for the post-module summative assessment that can be found at the Water, Agriculture, and Sustainability Assessment page.

References and Resources

Diaz, R.J and Rosenberg, R. (2008). Spreading Dead Zones and Consequences for Marine Ecosystems, Science, Vol. 321 no. 5891 pp. 926-929

Osmond, D.L., Meals, D.W., Hoag, D. LK., and Arabi, M., eds. (2012). How to Build Better Agricultural Conservation Programs to Protect Water Quality: The National Institute of Food and Agriculture–Conservation Effects Assessment Project Experience. Ankeny, IA: Soil and Water Conservation Society.

Committee on Environment and Natural Resources (2010), Scientific Assessment of Hypoxia in U.S. Coastal Waters. Interagency Working Group on Harmful Algal Blooms, Hypoxia, and Human Health of the Joint Subcommittee on Ocean Science and Technology. Washington, D.C.

National Science and Technology Council (2003), An Assessment of Coastal Hypoxia and Eutrophication in U.S. Waters

US EPA (2003), National Management Measures to Control Nonpoint Source Pollution from Agriculture EPA 841-B-03-004, July 2003 website. Hypoxia in the Northern Gulf of Mexico

NOAA Hypoxia information website

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These materials are part of a collection of classroom-tested modules and courses developed by InTeGrate. The materials engage students in understanding the earth system as it intertwines with key societal issues. The collection is freely available and ready to be adapted by undergraduate educators across a range of courses including: general education or majors courses in Earth-focused disciplines such as geoscience or environmental science, social science, engineering, and other sciences, as well as courses for interdisciplinary programs.
Explore the Collection »