Unit 2.2: Basic Critical Zone Concepts

Introduction

You will learn about geoscience-specific methods used to analyze data in the Critical Zone from data-driven activities and short presentations. The topics include the use of carbon isotopes, rock and soil profile weathering rates, stream discharge, demographics, and soil carbon. Activities will build data analysis and communication skills while using real data to interpret Critical Zone processes and begin to think about human interactions in the Critical Zone. The activities include geoscience-specific methods that can be used when developing your research proposal for the summative assessment activity. In this unit, you will:

• read short reports and analyze data to extract, organize and present a summary of that information
• critically examine geoscience methods and their potential application to Critical Zone science

Background

Although each Critical Zone Observatory (CZO) pursues unique research questions, hypotheses and experimental designs, the CZO network aims to collect common measurements that can be used to compare CZ processes and function across all sites. In effect, common measurements mean the sum of the network is greater than its parts (http://criticalzone.org/national/infrastructure/a-common-approach-1national/).

All U.S. CZOs seek to quantify, through a common set of measurements:

1. CZ structure and evolution

2. Event-based and continuous fluxes across CZ interfaces

3. Changes in budgets, including energy, water, solutes and sediment

To accomplish this, CZOs are working to collect the following data at as many sites as possible:

1. Land-Atmosphere

• LiDAR datasets
• Eddy flux for momentum, heat, water vapor, CO2 exchanges
• Wind speed and direction (sensors)
• Solar radiation and temperature (sensors)
• Precipitation and through-fall (samplers)
• Wet and dry deposition (samplers)

2. Vegetation and associated microbiota

• Above- and below-ground vegetative and microbial biomass
• Relations between ET and species composition and structure
• Soil/plant respiration, net ecosystem exchange

3. Soil (vadose zone)

• Solid phase (campaign sampling for spatial characterization)
• Texture and physical characterization
• Organic matter content
• Elemental composition and mineralogy
• Stable and radiogenic isotope composition
• Fluid phase (sensors and samplers for time series)
• Soil moisture (sensors)
• Soil temperature (sensors)
• Soil solution chemistry (samplers)
• Soil gas chemistry (samplers/sensors)
• Rates of infiltration and groundwater flow

4. Saprolite and bedrock (saturated zone)

• Solid phase (campaign sampling for spatial characterization)
• Texture and other physical and architectural traits
• Petrology and mineralogy
• Elemental composition and organic matter content
• Fluid phase (sensors and samplers for time series)
• Potentiometric head and temperature (sensors)
• Groundwater chemistry (samplers/sensors)
• Gas chemistry (samplers/sensors)

5. Surface water

• Discrete and instantaneous discharge (flumes, weirs, stage sensors)
• Channel morphology
• Stream water chemistry, dissolved and suspended (samplers/sensors)
• Sediment and biota (samplers/sensors)

More information about common measurements, including a matrix showing which observatories currently collect various measurements, can be found in the 2015 CZO common measurements white paper CZO common measurements white paper (Acrobat (PDF) 239kB Jan19 17). Measurements such as those collected at CZOs form the foundation for some of the CZ methods employed in the following exercises.

Unit 2.2: Basic Critical Zone Concepts

Part 1 - Geoscience-specific Methods

In-class

• Activities will be assigned to groups from a variety of methods including carbon isotopes, soil carbon, weathering rates, biogeochemistry, demographics, or stream discharge. Your group will work through the assigned activity and prepare a brief (5-10 min) presentation to report back to the class on what you found, including the following elements in your presentation:
• What is the main idea?
• How does this method work?
• What kind of results were obtained using this method?
• How is the data analyzed? Where should it be used ? Over what timescales is it useful?
• What are its advantages and disadvantages?
• What are the limitations to this method of analysis?
• How is this relevant to the Critical Zone?

Your instructor will assign activities from the following options:

1. CARBON ISOTOPES: This is a series of exercises investigating the role of sediments and sedimentary rocks in the global carbon cycle and the use of stable carbon isotopes to reconstruct ancient sedimentary environments. You will make some simple calculations and think about the implications of your results.
• Carbon Isotopes Activity Summary Carbon isotopes summary (Microsoft Word 2007 (.docx) 15kB Feb22 17)
• Carbon Isotope Worksheet Carbon Isotopes worksheet (Microsoft Word 58kB Dec23 16)
• Carbon Burial Worksheet Carbon Burial Worksheet (Microsoft Word 83kB Dec23 16)
• Carbon Particle Size Worksheet Carbon Particle Size Worksheet (Microsoft Word 20kB Dec23 16)
2. SOIL CARBON: How can the carbon in a dead, rotting rabbit or rotting leaves end up in the atmosphere? To understand this important carbon cycle question, you will need to understand the following about soil—what lives in soil, what soil is made of, and how soil behaves under different environmental conditions.
• Soil Carbon Activity Summary Soil carbon summary (Microsoft Word 2007 (.docx) 15kB Feb22 17)
• Background information: EarthLabs, Lab5a: Soil and the Carbon Cycle
• Bekku, Y.S., Nakatsubo T., Kume A., Adachi M. and Koizumi H. 2003. Effect of warming on the temperature dependence of soil respiration rate in arctic, temperate and tropical soils. Applied Soil Ecology. 22:205-210.
3. WEATHERING RATES: Atmospheric (and precipitation) chemistry determines the rate of weathering for marble tombstones and your task is to calculate weathering rates from tombstone weathering data.
• Weathering Rates Activity Summary weathering summary (Microsoft Word 2007 (.docx) 15kB Feb22 17)
• Sydney weathering data Sydney weathering data (Excel 2007 (.xlsx) 10kB Oct4 16)
• Wollengong weathering data Wollengong weathering data (Excel 2007 (.xlsx) 10kB Oct4 16)
• Dragovich S.D. 1986. Weathering rates of marble in urban environments, eastern Australia. Z. Geomorph. N. F. 30:203-214.
4. BIOGEOCHEMISTRY: You will use elemental chemistry data in a soil profile to explore major biogeochemical processes that dominate in the critical zone. Data will be provided for you to calculate and graph the mass transfer coefficients as a function of depth using Excel. Based on these plots, you can make generalized statements about how different elements behave in this soil profile and what processes dominate, e.g., depletion by rock-water interaction, addition by dust inputs or elemental loading by human activities etc.
• Biogeochemistry Activity Summary Biogeochemistry summary (Microsoft Word 2007 (.docx) 15kB Feb22 17)
• Biogeochemistry data Biogeochemistry Data (Excel 2007 (.xlsx) 16kB Dec23 16)
• Jin, L., Ravella R., Ketchum B., Bierman P.R., Heaney P., White T., and Brantley S.L. 2010. Mineral weathering and elemental transport during hillslope evolution at the Susquehanna/Shale Hills Critical Zone Observatory. Geochimica et Cosmochimica Acta 74:3669-3691.
• Brantley, S.L., Goldhaber M.B. and Ragnarsdottir K.V. 2007. Crossing disciplines and scales to understand the critical zone. Elements 3:307-314.
5. DEMOGRAPHICS: Hosted by the Council on Environmental Quality (CEQ), this site contains updated monthly tables with statistics about United States environmental quality. The major topics covered in these tables are population, economy and the environment, public lands, ecosystems, air quality, aquatic resources, terrestrial resources, pollution prevention, energy, transportation, and the global environment. The tables indicate data sources and an archive of statistics for earlier years is provided. Your task is to use the data to derive interesting visualizations and relationships among variables.
• Demographics Activity Summary Demographics summary (Microsoft Word 2007 (.docx) 15kB Feb22 17)
6. STREAM DISCHARGE: You will use USGS data to compare the discharge per unit area in July for a pair of nested watersheds in the high country of Glacier National Park. The calculation illustrates how discharge per unit area varies with elevation and demonstrates the distinction between extensive quantities (discharge) and intensive quantities (discharge/area). The module also introduces the hydrologic concepts of watershed, stream discharge, and orographic precipitation.
• Stream Discharge Activity Summary Stream discharge summary (Microsoft Word 2007 (.docx) 15kB Feb22 17)

Part 2 - Group Method Reports

In-class

• Each group will provide a 5-10 minute presentation for the class and will be assessed by the instructor and their peers on how effectively the science and methods are communicated.

• Class Presentation Rubric (Microsoft Word 18kB Dec23 16)
• Student Peer Presentation Review Rubric (Microsoft Word 29kB Dec23 16)