Lake Mixing Module

This module was initially developed by Carey, C.C., J.L. Klug, and R.L. Fuller. 1 August 2015. Project EDDIE: Dynamics of Lake Mixing. Project EDDIE Module 3, Version 1. cemast.illinoisstate.edu/data-for-students/modules/lake-mixing.shtml. Module development was supported by NSF DEB 1245707.

Summary

Stratified lakes exhibit vertical gradients in organisms, nutrients, and oxygen, which have important implications for ecosystem structure and functioning. Mixing disrupts these gradients by redistributing these materials throughout the water column. Consequently, it is critical to understand the drivers of lake mixing and thermal stratification, especially because of the sensitivity of lake thermal conditions to altered climate. In this module, students will explore spatial and temporal patterns of lake mixing using high-frequency temperature data from lakes around the world. They will also explore how increases in air temperature affect thermal stratification by interpreting output from a lake model. Project EDDIE modules are designed with an A-B-C structure to make them flexible and adaptable to a range of student levels and course structures.

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Learning Goals

  • Interpret variability in lake thermal depth profiles over a year.
  • Identify lake mixing regimes based on visualization of water temperature data.
  • Compare and contrast lake mixing regimes across lakes of different depths, size, and latitude.
  • Understand the drivers of lake mixing and thermal stratification.
  • Predict how climate change will affect lake thermal stratification and mixing.

Context for Use

This entire module can be completed in one 3 hour lab period for introductory students or two 60 minute lecture periods for intermediate-level students. Activities A and B could be completed with upper level students in one 60 minute lecture period. Students will need 1-2 hours outside of class to prepare for the exercise and complete the homework activities.

This module has been used in several Freshwater Ecology and Limnology courses (Parts A and B for lower-level courses; Parts A, B, and C for upper-level courses). Module materials can be tailored to increase or decrease the background information depending on students' quantitative skills.

Description and Teaching Materials

Quick overview of the activities in this module

See the teaching materials files, provided below, for a step-by-step description for carrying out this module. A student handout, describing Activities A, B, and C, and instructor answer key are also provided.

  • Activity A: Understanding and identifying different lake mixing regimes, based on visual representations of data
  • Activity B: Patterns and variability in lake stability, time series graphs
  • Activity C: Analyze output data from a general lake model to examine the effect of future increases in temperature on lake thermal profiles.

Workflow for this module:

  1. Assign pre-class reading.
  2. Give students their handout when they arrive to class: Student Handout (Microsoft Word 2007 (.docx) 952kB Dec27 16), Student Dataset (Excel 2007 (.xlsx) 4.5MB Dec27 16), and Lake Mixing Figures (Microsoft Word 980kB Dec27 16)
  3. Discuss pre-class readings.
  4. Instructor gives brief PowerPoint presentation on heat dynamics in lakes - Lake Mixing Module: Instructor's PPT (PowerPoint 7.1MB Dec27 16)
  5. As part of the presentation, the instructor gives a demonstration on how to interpret temperature and stability data from Lake Sunapee, New Hampshire, USA.
  6. After the presentation, the students divide into teams and discuss temperature patterns and the mixing regime for an individual lake (Activity A).
  7. The instructor then leads a discussion of Activity A and introduces Activity B.
  8. Students plot and interpret stability for an individual lake and compare across lakes using class data (Activity B).
  9. The instructor then leads a discussion of Activity B and introduces Activity C.
  10. Students use output from models simulating elevated air temperature to explore the effect of climate change on lake temperature and stability (Activity C).

Teaching Materials:

Teaching Notes and Tips

See the Instructor's Manual (Microsoft Word 2007 (.docx) 891kB Dec27 16) and Instructor's PowerPoint (PowerPoint 7.1MB Dec27 16) for notes and tips for carrying out this exercise.

Assessment

In Activity A, students use visual representations of data to understand and identify different lake mixing regimes.

In Activity B, students look at patterns and variability in lake stability, time series graphs.

In Activity C, students analyze output data from a general lake model to examine the effect of future increases in temperature on lake thermal profiles.

Notes, tips, and an answer key are provided in the following files:

References and Resources

Required pre-class reading

  • O'Reilly, C.M., S.R. Alin, P.-D. Pilsnier, A.S. Cohen, and B.A. McKee. 2003. Climate change decreases aquatic ecosystem productivity of Lake Tanganyika, Africa. Nature 424:766-768.

Discussion of paper: You can have students come up with their own research questions as part of the pre-class assignment. Sample questions include: What factors have led to a change in stratification (thermal stability) over time in Lake Tanganyika? Why does stratification have an effect on productivity in Lake Tanganyika?