Creatures Under Foot: Soil Chemistry and Microscopic Animals

Overview

Students will collect soil samples and analyze them with some of the same procedures used by researchers in the McMurdo Dry Valleys, Antarctica. Soil microfauna (e.g. nematodes) will be extracted from the samples using a Baermann funnel. Students will compare their own data to published data from researchers working in Antarctica.

Objectives

• Collect and analyze soil samples for moisture, pH, and electrical conductivity.
• Use a Baermann funnel to extract soil microfauna (e.g. nematodes).
• Observe, identify (morphospecies) and count the extracted animals.
• Analyze a published data set and compare the results to student-collected data.

Lesson Preparation

• Prior to the lab students need to be able to use stereomicroscopes.
• Prior to the lab analysis students need to know how to use a spreadsheet to organize data and perform basic calculations.
• Print copies of the Soil Chemistry and Microscopic Animals Worksheet (in Lesson Materials).
• Students will need access to the research paper listed under Resources.
• Prepare counting dishes by printing the Grid for Nematode Counting file (in Lesson Materials) on a transparency sheet. Cut out the grid blocks and attach them to the bottom of 60 mm petri dishes.
• Collect soil samples for use in class or have students bring their own samples.

Procedure

1. Collect, or assign students to collect, soil samples in one-quart zip-top plastic bags. Ideally, soil samples should be refrigerated until the lab period. Soil can be collected with a hand garden trowel.
2. Measure 50 grams of each soil sample into a pre-weighed soil can and follow the procedure for Gravimetric Soil Moisture outlined on page 4 of the Standard Procedures for Soil Research in the McMurdo Dry Valleys LTER document which is linked to under Resources.
3. Measure 20 grams of soil into a 150 ml beaker and follow the procedure for Soil pH outlined on page 5 of the Standard Procedures for Soil Research in the McMurdo Dry Valleys LTER document.
4. Prior to measuring the electrical conductivity of your sample, measure the conductivity of a 0.01M KCl standard so you will be able to adjust conductivity for your laboratory environment. After measuring the pH add an additional 60 ml of di-H20 to the sample in the beaker and follow the protocol for measuring electrical conductivity on page 5 of the Standard Procedures for Soil Research in the McMurdo Dry Valleys LTER document.
5. Set up Baermann funnels and add some water to test for leaks; instructions for constructing Baermann funnels can be found by following the links listed under Resources. Place 50 grams of soil on top of a lotion-free facial tissue suspended on the wire mesh in the Baermann funnel. Fold in the sides of the tissue and fill the funnel with additional water to cover the soil sample.
6. After 24 hours open the clamp on the Baermann funnel to collect 10-20 ml of water into a conical tube or a nematode counting dish.
7. Make observations of the nematodes and other microfauna. Use size, shape and movements of the nematodes to identify morphospecies. Count and record the nematodes recovered from each soil sample.
8. Use the published description of the distribution of nematodes in Victoria Land, Antarctica to predict the soil chemistry where each of the three common nematodes (Scottnema, Eudorylaimus, and Plectus) would be found (Adams et al. 2014).
9. Use data from the Soil Elevational Transect Experiment to test your predictions by calculating the mean soil moisture, pH and electrical conductivity for samples containing each of the three nematode species found in the McMurdo Dry Valleys. There is a link to the data under Resources.
10. Compare student collected data to the analyzed data from the McMurdo Dry Valleys.

Extension

• The Data Analysis and Comparisons portion of the activity could be eliminated to shorten the activity or if computers are unavailable.
• Inquiry modifications – if enough soil is collected, students could experiment with the Baermann funnel protocol (type of tissue used or cheese cloth, length of time, etc.) to compare nematode yields.
• Additional Data Analysis – After calculating means for each of the three soil parameters for each of the three nematode species combinations in the McMurdo Dry Valleys, students can graphically represent the data and calculate standard deviation and standard error for the samples. Additional variables from the data set could also be analyzed.

Resources

Links for Lab Protocols, Data, and Information

• Baermann Funnels – American Phytopathological Society
• Baermann Funnels – Tylka Lab at Iowa State University
• Baermann Funnels – Nematode-Plant Expert Information System
• MCM LTER Soil Chemistry Protocols
• MCM LTER Soil Elevational Transect Experiment Data
• Tough Tardigrades PolarTREC Journals The entries for Nov. 7th, 2016 and Jan 5th, 6th, 9th, and 19th, 2017 will be useful.

Research Paper for the Activity

Adams, B. J., Wall, D. H., Virginia, R. A., Broos, E., & Knox, M. A. (2014). Ecological biogeography of the terrestrial nematodes of Victoria Land, Antarctica. ZooKeys, (419), 29-71. doi:10.3897/zookeys.419.7180

Assessment

Soil Chemistry and Microscopic Animals Worksheet found in Lesson Materials.

Author/Credits

Josh Heward (josh.heward [at] gmail.com)

This material is based upon work supported by the National Science Foundation Grant #OPP-1637708 for Long Term Ecological Research. Any opinions, findings, conclusions, or recommendations expressed here are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.