Initial Publication Date: October 11, 2006

Lake Pontchartrain: Sediment Sampling

Created by David Patterson & Sarah Bordenstein, Marine Biological Laboratory

In this activity, students will:

Learn how to collect microbes from sediment samples
Use a microscope to observe and record major groups of environmental microorganisms

Materials Needed

Day 1: Prepare Environmental Sample

Collect mud or sand samples from Lake Pontchartrain in an area where the water is about 1 foot deep. Collect just the surface sediments (black sediments are bad!). Place samples in bucket and layer with about an inch of water.
Transport samples to the classroom and sieve onto shallow dishes - such as disposable plastic food containers.
Leave the sample for 10 minutes. Using a disposable pipette, remove water from the top of the samples to a beaker until the sediment is damp but with no sloshing water. (The excess water may later be used to make a wet mount.)
Place one sheet of lens paper directly on top of the samples and put about six cover slips (22 X 22 mm No 1's are best) on top of each lens paper. Place a lid loosely on top of the container. Over the next two or three days, bottom of the sediments will become anoxic and the microorganisms will migrate from the sediment, through the lens paper, and up to the coverslip. You can then lift the coverslips carefully off the sediment to look at the mnicrobial community that has accumulated.

Day 3 or 4: Make a Wet Mount

Using ridged forceps, gently lift a coverslip from the top of the sediment. The coverslip should already be wet enough to prepare a wet mount. If it is too dry, add a drop of excess water from the sample onto the microscope slide.
While holding the coverslip upright, carefully touch one edge on the slide.
Trying to minimize the amount of air bubbles under the coverslip, slowly and gently lower it facedown onto the slide. (Hint: if your slide is too wet, the coverslip will fall off when you tilt it horizontally.)
Put the slide on a microscope, and starting with lowest magnifications to help orient yourself, navigate around to find as many kinds of microbes as you can (e.g., bacteria, diatoms, ciliates, and amoebae).
Make sketchs of the organisms observed. If available, use videos or cameras to create 'uninterpreted' records of what you see.

Download Student Handout (Microsoft Word 34kB Oct11 06)
micro*scope: Images, descriptions and taxonomic classification of microorganisms.
Protistiary: Comprehensive online textbook of protocols and references pertaining to Protists.
Sampling Muds: This Protistiary protocol describes how to sample exposed sediments (mud & sand).
Lake Pontchartrain Resources: Collection of news articles, environmental reports, educational activities and scientific literature dedicated to Lake Pontchartrain.
Introduction to Optical Microscopy, Digital Imaging, and Photomicrography

SI-H-A3 (Science as Inquiry, The Abilities Necessary to do Scientific Inquiry): Using technology and mathematics to improve investigations and communication.
LS-H-A1 (Life Science, The Cell): Observing cells, identifying organelles, relating structure to function, and differentiating among cell types.
LS-H-C4 (Life Science, Biological Evolution): Classifying organisms.
LS-H-C5 (Life Science, Biological Evolution): Distinguishing among the kingdoms.