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Unit 4.2 - Carbon Budgets

Jim Washburne (University of Arizona)

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Summary

The purpose of this unit is to explore, compare, contrast, and interpret carbon fluxes from the Ameriflux network to better appreciate the critical factors that account for the different timing and magnitudes of fluxes among these sites. This module will help students complete their semester-long project by introducing them to critical baseline data collection and databases related to carbon budgets.

The primary data set for this activity is the Amerflux network database, which spans over 150 sites throughout the Americas. Each data set is uniformly formatted and can contain up to 45 fields of meteorological and flux data collected from various eddy correlation tower instruments. The lesson is divided up between the following engaging activities:

  • Background lecture: Introduction to carbon fluxes and balances
  • Discovery Activity: Students in small groups will compare various annual flux records from four different sites to address questions regarding driving variables, correlation among variables, and causative factors responsible for the overall trend in annual CO2 flux. Group results will be shared and discussed by the whole class as time allows.
  • Database Access Activity: Students will learn what data exists in the Ameriflux data base and how to load it into an Excel spreadsheet for display using an Amerflux site that also is part of the CZO network.
  • Carbon Flux Hypothesis Activity: Students will develop a simple hypothesis regarding the timing and/or magnitude of CO2 fluxes and use data from the Ameriflux database to support their ideas.

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Learning Goals

This unit guides students to analyze carbon flux data collected at various scales to understand the regional exchange of carbon at an Ameriflux or CZO site. This relates to the grand challenge of understanding atmospheric gases and biogeochemical/carbon cycling. This unit also relates to the geoscience literacy themes of Earth system changes that occur at multiple scales and the interconnections between the carbon and energy and water cycles.

Students will:

  • Use a carbon cycle diagram to discuss the different pathways of carbon at a watershed scale.
  • Contrast global and biome-specific carbon budgets to better understand watershed-scale processes.
  • Relate carbon flux data collected at various scales to understand the regional exchange of carbon at an Ameriflux site.
  • Explore and visualize carbon flux data from the Ameriflux database.
  • Use carbon flux data from the Ameriflux database to support a simple hypothesis relating carbon flux to driving environmental variables.

Context for Use

This week-long unit for advanced undergraduates/graduates explores Critical Zone carbon flux data and models during two 75 minute class periods. This module, "Land-Atmosphere Exchanges," is part of the InTeGrate interdisciplinary course called "Introduction to Critical Zone Science." The physical basis will be introduced quickly, followed by prevailing theories or analytical perspectives so that at least half of each class period can be spent examining and analyzing Critical Zone data sets.

Description and Teaching Materials

Unit 4.2.1 - Day 3 (75 minutes total)

Day 3 - Lesson Plan Overview

  • Assign background reading to students at the end of the previous class.
  • Discovery Activity: Examining Annual Carbon Flux Graphs (25 min) - The purpose of this exercise is for the students to compare and contrast data from four eddy correlation measurement sites to discover and think about the causal or physical relationships among these variables. We do this prior to a formal introduction to the measurement technique to more fully engage their powers of observation and inquiry.
    • Introduction & Setup ( 3 min) - One way to introduce this activity is to say: "The purpose of this exercise is for you to compare and contrast carbon data from four eddy correlation measurement sites to discover and think about the causal or physical relationships among these variables. We will talk more about eddy correlation and data networks later in this unit. Note that not all these sites have the same kind of vegetation. Most of the graph variables will hopefully be familiar from Unit 4.1. This is real data so expect a certain amount of ambiguity. What you need to do over the next 10-15 minutes is to get in small groups, read the handout and answer the discussion questions as a group. Be prepared to share observations and discuss your answers with the rest of the class later. Your primary task is to look for parameters that are correlated (have the same general shape or trends) and to think about and look for factors that might control the magnitude of the CO2 flux (FC). Focus primarily upon relationships between the parameters for a single site; although you might also see consistent patterns from one site to another. The bottom-line question we will be addressing throughout this unit is "What controls the annual shape of the carbon flux curve?"
    • You might want to quickly shuffle through the set of graphs on a classroom display to briefly describe the layout of the graphs, although most of this information is described on page two of the worksheet.
    • Break the class into groups of two to four students. Hand out a set of four carbon flux graphs to each group.
    • Small group exploration (15 min) -
    • Class discussion (10 min) - The worksheet key (see Assessments) highlights some of the relationships your students might observe but there will undoubtedly be others. There is also a set of annotated graphs below that highlight some of the relationships between energy and carbon fluxes. Some students might misinterpret a relationship between some variables. Try to point out some complicating factors or suggest they think about the problem more physically, which might resolve the misunderstanding. This discussion could obviously be extended if you have the time.
  • Energy Budget - There are 30 slides so you will have to move briskly.
  • Exploring & Working with the Ameriflux (AMF) Database: Carbon Flux Graphing Activity (25 min) - For homework, the students just have to demonstrate that they can plot a few of the major fluxes from one site, called "AMF_USvcp_2008". The bigger assignment for the following evening is to actually form a simple hypothesis and try to find some supporting data using this ability to visualize the data. It's never too early to get started forming a hypothesis and looking at other data sets so encourage the students to move forward with the assignment and bring their questions to class.
    • Introduction & Setup (5 min) -These slides walk the class through what the database will look like and what they need to do with the data that they download.
    • In-class - Small group focus (15 min) - Have the students start exploring the Ameriflux database by examining metadata that is crucial to understanding the data record.
      • WARNING - this will require computer browser connectivity for each group. If you don't have computer access, you will have to print this file out and distribute 1 set/group. Note: the data columns are numbered for convenience.

Day 3 - Instructions and Materials

Activity 4.4 - Examining Annual Carbon Flux Graphs

Discovery Activity: Examining Annual Carbon Flux Graphs (25 min) - The purpose of this exercise is to compare and contrast data from four eddy correlation measurement sites to discover and think about the causal or physical relationships among these variables. Directions - Examine the four graphs in Table 4.2.1 (below) and look for critical relationships between the parameters.

Introduction to Carbon Cycles & Budgets Lecture (25 min) - The purpose of these slides are to tie the motivation for monitoring CO2 back to the bigger issue of global climate change and to highlight some of the key understandings we have of the carbon cycle and what the flows of carbon are at the global scale. The slides also start to introduce some of the plant physiological factors that affect the magnitude of the carbon flux.

  • Standard Lecture - Introduction to Carbon Cycle & Budgets (28 slides, ~25 min)
    • Student Lecture Notes, Carbon Cycle and Budgets, Printable (6/pg) Student Note Set (Acrobat (PDF) 1.5MB Feb25 17)
    • Instructor Lecture Slides, Carbon Cycle and Budgets Instructor Slide Set (PowerPoint 2007 (.pptx) 4.2MB Feb26 17);

Activity 4.5 - Carbon Flux Graphing

Exploring & Working with the Ameriflux (AMF) Database: Carbon Flux Graphing Activity (25 min) - The ultimate goal here is to actually work with typically archived carbon flux data. For convenience, we have selected the Ameriflux network (which has limited overlap with the CZO network). In-class - Start exploring the Ameriflux database and examine metadata that will be crucial to understanding the data record.

  • Exploring the Ameriflux Database (12 slides, ~15 min)
    • Student Lecture Notes: The Ameriflux Database - Printable (6/pg) Student Note Set (Acrobat (PDF) 702kB Feb25 17)
    • Instructor Lecture Slides: The Ameriflux Database Instructor Slide Set (PowerPoint 2007 (.pptx) 9.7MB Feb25 17)
    • Handout - Keeling Curve (Acrobat (PDF) 196kB Sep26 13)
  • Working with the Ameriflux Database
  • Supporting Handouts
  • Homework - This homework is more fully described in the Student Worksheet (above). In order to give you broader exposure to a high quality Carbon flux dataset and because of network‐to-network inconsistencies in the CZO data set, we will focus our initial data manipulations on the excellent Ameriflux network with over 150 sites throughout the Americas. Once you have experience with this data set, it is fairly easy to address similar questions with the CZO data set. As a challenge, look at a different data set than the one covered in class and produce two labeled graphs demonstrating you can visualize this data set using Excel or Matlab.
    • Graph 1: Carbon fluxes - FC and Re
    • Graph 2: Energy fluxes - Rn, H, LE

Unit 4.2.2 - Day 4 (75 minutes total)

Day 4 - Lesson Plan Overview

  • Luyssaert Article Discussion (5 min)
    • Some of this material is copyrighted so links are provided to the original materials. You might bring a graphic to class of his basic carbon flux diagram so you can discuss how it changes in different settings.
  • Introduction to Eddy Correlation & Modeling Lecture (20 min)
    • Some of this material is copyrighted so links are provided to very useful support documents.
  • Carbon Flux Hypothesis Activity (30 min) - The purpose of this activity is to tap into students' ecologic knowledge and relate these ideas to actual data collected across a wide range of biomes. This will be tricky to do working with 30 min interval data in Excel. I have used Matlab to write out the daily average data that was plotted in the Discovery Activity (Table 4.2.1). It is also possible to use daily average data from the CZO database. One way to get started is to have the students think about the four biomes we looked at originally (Rockies Ponderosa Forest, High Plains Grassland, Appalachian Deciduous Forest, and Canadian Pine Forest and consider what factors control plant growth. Note that there is a larger set of Ameriflux site graphs below in resources.
  • Open question & answer period regarding CO2 Hypothesis and Site selection (10 min)

Instructions and Materials

  • Pre-class reading Assignment
  • Review and Discuss previous class's activities and homework (5 min)

The standard method of measuring hillslope scale carbon fluxes is based on the Eddy-correlation Method. This lecture and supporting material highlights this critical tool and source of some of the CZO data we are dealing with.

  • Standard Lecture: Introduction to Eddy Correlation & Modeling (17 slides, ~20 min)
  • Support - Please review the following source material
    • Download and review sections 2.6, 2.7, 3.2, 4.11 in Burba, G., 2013. Eddy Covariance Method for Scientific, Industrial, Agricultural, and Regulatory Applications: A Field Book on Measuring Ecosystem Gas Exchange and Areal Emission Rates. LI-COR Biosciences, Lincoln, NE, USA, 331 pp.
      https://www.licor.com/env/products/eddy_covariance/resources.html
    • Download and review lectures 3, 8 in Baldochi's ESPM Class notes for Advanced Topics in Micromet and Biomet.
      nature.berkeley.edu/biometlab/index.php?scrn=espm228

Activity 4.6 - Carbon Flux Hypothesis

Carbon Flux Hypothesis Activity (30 min) - The purpose of this activity is to connect physical factors that might affect ecosystem productivity with the flux data available from the CZO or Ameriflux databases. One way to get started is to have the students think about the four biomes we looked at originally (Rockies Ponderosa Forest, High Plains Grassland, Appalachian Deciduous Forest, and Canadian Pine Forest and consider what factors control plant growth.

  • Working with the Ameriflux Database - Carbon Flux Hypothesis Activity
  • Supporting Materials
    • Introduction - Trivial relationship between Ta and Ts and other Examples (Acrobat (PDF) 556kB Jan29 17)
    • Homework - Form a simple hypothesis regarding factors affecting the CO2 flux and support using Ameriflux data
  • Open question & answer period regarding CO2 Hypothesis and Site selection (10 min)

Ameriflux Field Site Flux Tower Graphs

Daily .xls files
Vcp: Valles Caldera - Ponderosa Pine, NM
Marcy Litvak AmeriFlux US-Vcp Valles Caldera Ponderosa Pine, doi:10.17190/AMF/1246122
http://dx.doi.org/10.17190/AMF/1246122 		Vcp2007 (Acrobat (PDF) 44kB Sep24 13) VcpDaily (Excel 113kB Oct4 13)
Kon: Konza Prairie, KS
Nathaniel Brunsell AmeriFlux US-Kon Konza Prairie LTER (KNZ), doi:10.17190/AMF/1246068
http://dx.doi.org/10.17190/AMF/1246068		 Kon2012 (Acrobat (PDF) 43kB Sep24 13) KonDaily (Excel 112kB Oct4 13)
WBW: Walker Branch Decid. Forest, TN
Tilden Meyers AmeriFlux US-WBW Walker Branch Watershed, doi:10.17190/AMF/1246109
http://dx.doi.org/10.17190/AMF/1246109		 WBW2001 (Acrobat (PDF) 40kB Sep24 13) WBWDaily (Excel 104kB Oct4 13)
NS5: Manitoba Pine Forest, Can
Mike Goulden AmeriFlux CA-NS5 UCI-1981 burn site, doi:10.17190/AMF/1246002
http://dx.doi.org/10.17190/AMF/1246002		 NS52004 (Acrobat (PDF) 39kB Sep24 13) NS5Daily (Excel 109kB Oct4 13)

Citation: Ameriflux Network, ameriflux.lbl.gov


Assessment

  • In-class participation (~ 10 pts)

Activity 5 - Groups look at eddy correlation flux data and make some simple observations about apparent correlation and factors affecting the CO2 flux. Five discussion questions help them focus on important issues and serve as a useful formative evaluation of small group understanding. The answers provided here are exemplary. There is no one right answer.

  • Carbon Discovery (15 pts)

Activity 6 - Students explore and visualize carbon data from the Ameriflux database. Questions 1-8 in the worksheet are designed to get the student thinking about driving forces behind CO2 fluxes. Question 9-11 are more quantitative and serve as important "back-of-the-envelope" calculations for assessing global scale carbon reservoirs. Filling out the table of data set variable names may seem tedious, but there is no better way to start becoming conversant with these variables. The students will produce two graphs of interest from the Ameriflux data set.

  • Carbon Flux Graphing (15 pts)
  • Graphs should be evaluated using the Graph Grading Rubric (Microsoft Word 2007 (.docx) 17kB Dec23 16). (15 pts)

Activity 7 - Students now combine their ability to manipulate the database and connect carbon fluxes with biospheric forcings to make reasonable yet simple hypotheses related to the timing and magnitude of the CO2 flux. The graphs or tables they produce for this homework will be more varied and thus more difficult to access but the emphasis should be on how well they were able to seek the appropriate data and express or display their results. Some hypotheses are not easily verified and may even be disproved by the data accessible to the student so this should not count against the student if the assignment was done well in other respects.

  • Carbon Flux Hypothesis
  • Carbon Flux Hypothesis Grading Rubric (Microsoft Word 2007 (.docx) 17kB Dec23 16) (15 pts)

References and Resources

Activities

Sources of Data

Background Materials

Example data sets - Ameriflux Data (averaged and plotted by Washbune for InTeGrate, 2013)

Site

 Flux Tower Graphs

Full Set of 15 carbon Flux Graphs (9/pg)

CarbonFluxSet (Acrobat (PDF) 458kB Sep21 13)

Sa1: LBA Tapajos Mature Tropical Forest

Sa3: LBA Tapajos Logged Tropical Forest

Sa12005 (Acrobat (PDF) 33kB Sep21 13)

Sa32003 (Acrobat (PDF) 32kB Sep21 13)

NR1: Niwot Ridge Evergreen Alpine, CO

NS5: Manitoba Evergreen Forest, CN

Fuf: Flagstaff Evergreen Forest, AZ

NR12007 (Acrobat (PDF) 35kB Sep21 13)

NS52007 (Acrobat (PDF) 35kB Sep24 13)

Fuf2007 (Acrobat (PDF) 37kB Sep21 13)

SP1: Austin Cary Pine, FL

ME2: Metolius Interm. Pine, OR

KS2: Kennedy Space Ctr Scrub Oak, FL

SP12006 (Acrobat (PDF) 34kB Sep21 13)

ME22007 (Acrobat (PDF) 35kB Sep21 13)

KS22006 (Acrobat (PDF) 36kB Sep21 13)

MMS: Morgan Monroe Decid. Forest, IN

WBW: Walker Branch Decid. Forest, TN

Ha1: Harvard Decid. Forest, MA

MMS2005 (Acrobat (PDF) 35kB Sep21 13)

WBW1999 (Acrobat (PDF) 48kB Sep21 13)

Ha12006 (Acrobat (PDF) 36kB Sep21 13)

Var: Vaira Ranch Grassland, CA

Wkg: WG Kendall Grassland, AZ

Var2007 (Acrobat (PDF) 34kB Sep21 13)

Wkg2007 (Acrobat (PDF) 36kB Sep21 13)

IB2: Fermi Prairie, IL

Wlr: Walnut River grasslands, KS

IB22006 (Acrobat (PDF) 35kB Sep21 13)

Wlr2003 (Acrobat (PDF) 35kB Sep21 13)

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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 »