Construction of a Simple Conceptual Model

Scott Werts, Winthrop University

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This homework assignment is designed to give the students practice in developing a simple conceptual model using reservoirs, fluxes, and simple calculations of sediment, carbon and nutrient accumulation in a typical reservoir/river system. This assignment is typically used after an introductory lecture to biogeochemical cycles and gives the students a concrete example of nutrient and sediment issues in surface water systems.

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I utilize this exercise in an introductory geochemistry course when introducing biogeochemical cycles.

Skills and concepts that students must have mastered

The students must be able to understand the basic concepts of reservoirs, fluxes, turnover times, residence times and other aspects of conceptual models.

How the activity is situated in the course

This is utilized as a homework assignment within the course. I typically give an overall introduction to conceptual models, then continue on to the carbon, nitrogen, sulfur and phosphorous cycle after this exercise is completed.


Content/concepts goals for this activity

This assignment is used to give students practice in organizing inputs, outflow, accumulations, fluxes and storage of sediments, nutrients and carbon in a spatial arrangement.

Higher order thinking skills goals for this activity

This is designed to get the students to extract data, organize their thoughts regarding the data and apply it directly to a basic model to trace the inputs to a river system. Students should be able to analyze the data and attribute inputs of sources from points along a river basin.

Other skills goals for this activity

Description and Teaching Materials

In this activity, students are to utilize sediment load and carbon, nitrogen and phosphorous content from a real system of aquifers and rivers in Kansas to construct a simple conceptual model regarding sediment and nutrient flow. Students are typically given this assignment for homework following a lecture on biogeochemical cycles. In the table on the first page of the assignment, I have already extracted the data they should need to complete the assignment. This data comes directly from two government reports, also provided to the students for download.

Student Assignment for Conceptual Model (Microsoft Word 328kB Apr25 13)
john_redmond_report (Acrobat (PDF) 6.6MB Apr25 13)

Teaching Notes and Tips

In submitting this assignment, I usually explain to the students that they will need to turn in two conceptual models. One containing the sediment flux and storage in the system and then another, that will look schematically the same, but will show nutrient and carbon loads. Usually, the sticking point is describing the regulated vs unregulated flow. They will need an extra reservoir and flux on their diagrams that is not seen on the map of the area to account for the influx of unregulated sediment and nutrients.


The assignment requires them to turn in two conceptual models (or one very organized one), a calculation or turnover time and a short justification for their calculation of turnover time estimates in the future. I usually have the students sketch a simple conceptual model on the following exam. I find this exercise is good practice for that.

References and Resources