Mud! 6th grade Science

Grade Level: 
Middle School

Mud, or sediment, is an active part of aquatic ecosystems.  Sediment varies widely within and among ecosystems in its biotic and abiotic characteristics.  In many ecosystems sediment can release excess  phosphorus (a common aquatic pollutant) into the water column causing internal eutrophication. 


At the conclusion of the lesson, students will be able to: 

Observe and describe abiotic and biotic characteristics of sediment 

Recognize that the sediment and water in a lake carry phosphorus, which is necessary for life, but can have negative ecosystem effects at high levels 

Describe the difference between experimental control and treatment groups 

Use observations to support conclusions 



One 45 min time frame (or longer with walk time added) 

About one week later, another 45 min to 60 min, which can be split into two days, if necessary  


NOTE:  Prior to the first day of the lesson, decide if the samples will be collected with a class “field trip” to a pond/stream (which will increase the time needed by the necessary travel time) or if the teacher will bring in pond water and pond mud samples.


This activity is appropriate for 6th grade where the subject of interactions between abiotic and biotic components of an ecosystem is introduced and high school biology in the context of biogeochemical cycles; the lesson can be modified to focus on earth materials for earlier grade levels 


MI High School Content Expectations 

B1.1D Identify patterns in data and relate them to theoretical models. 

B1.1E  Describe a reason for a given conclusion using evidence from an investigation. 

B 2.2B Recognize the six most common elements in organic molecules (C, H, N, O, P, S). 

B3.3b Describe environmental processes (e.g. the carbon and nitrogen cycles) and their role in processing matter crucial for sustaining life. 

MI Grade Level Content Expectations 

S.IP.06.13 Use tools and equipment (spring scales, stop watches, meter sticks and tapes, models, hand lens, thermometer, models, sieves, microscopes) 

appropriate to scientific investigations. 

L.EC.06.31 Identify the living (biotic) and nonliving (abiotic) 

L.EC.06.32 Identify the factors in an ecosystem that influence changes in population size. 


Use one set of jars for the whole class 

2-3 quart jars with lids 

Mud from a pond (enough for about 1/3 of each of the jars) 

Water from a pond--algae WILL be there (enough to fill the other 2/3 of each of the jars) 


For each pair of students: 

Compound microscope  

Microscope slides 




Dissolved oxygen meter 

Dissecting microscope 


Conductivity meter 

Water quality kits for measuring nutrients 


When studying aquatic ecosystems, people often think about the water and things that live in the water.  However, the mud at the bottom of lakes and wetlands, or sediment, is an active part of these ecosystems.  A wide diversity of organisms, both macroscopic and microscopic, live in sediments.  Sediments can often be a source of nutrients, especially nitrogen and phosphorus, to the water column.  Nutrients released from sediments are part of an ecosystem’s internal load (as opposed to the external load, which consists of nutrients that come from outside the ecosystems.)  Most commonly, sediments release large amounts of phosphorus as phosphate (PO43-), sometimes causing excessive algal growth, harmful algal blooms (growth by algae that produce toxins), and even fish kills (as dead algae fall to the bottom of an ecosystem, fuel bacterial decomposition, and consume oxygen).  These negative effects caused by sediment release of phosphorus are called internal eutrophication. 


First Day: 

Brainstorming Questions 

  As the class is walking to the pond, or as the teacher shows them pictures of a pond and the pond sediment and pond water collected previously, have the students consider the questions, “What does the pond water have in it?  What does the pond sediment (or the soil that makes up the pond’s floor) have in it?”  As you facilitate their brainstorming, you may want/need to encourage them to think on smaller scales (microscopic and atomic/molecular). 


  Lead the class in a discussion about how the abiotic and biotic components of the pond could interact.  Use what the students have said to link the nutrient content of the sediment and water to the activity of living things in the water.  For example, nutrients released from the sediment can enhance growth of algae in the water. 


Hypothesis Generating and Experimental Set Up 

 1.  Set up the jars: 

  a.  three with nothing but pond water in it (control group) 

  b.  another three jars with 1/3 pond sediment and 2/3 water in it (treatment) 

  c.  if possible a third set of jars with a different pond’s sediment set up like “b” 


 2.  Lead students through the process of developing a hypothesis with the guiding questions:  What differences do you expect to see in the treatment group and control group in about a week?  Why do you think those differences might occur? Possible hypothesis:  There will be a greater number of algae in jar with sediment and pond water compared to the jar with only pond water. 



Second Day: 

Check the jars after one week.  If you do not see obvious responses, check them again after two weeks as it may take some time for visible algal growth to occur. 


 1.  Qualitative Observations:  appearance of the water and sediment, look for evidence of algae growth—cloudy water and green “slime” on the sediment; any bubbles coming from the sediment, smell, layers in sediment evidenced by color difference or texture changes; macroscopic organisms in either sediment or water; bacterial growth (slime).  Use the “Field Guide to Mud” table (under “Resources in this document) and PowerPoint slides to help explain your qualitative observations 


 2.  Quantitative Observations:  use a microscope to count the algal cells in the water in each jar; if available, test the water in each jar with any available nutrient water testing kit (nitrogen and/or phosphorus), depth of water and sediment over time, water temperature, conductivity and dissolved oxygen, pH 


Data Analysis and Conclusions (if needed, this may be done on the next class day) 

 1.  lead students back to their hypothesis and model for them how the results may or may not support their prediction.  Emphasize the use of actual observations in their answers.  Ex:  The hypothesis “There will be a greater number of algae in jar with sediment and pond water compared to the jar with only pond water” was supported.  There were 100 algal cells counted in the jar with sediment but only 30 algal cells in the jar containing only water. 


2.  Discuss with the students their reasoning on why the results turned out the way they did.  If the results didn’t support the expected (we WOULD expect more algae to grow with the sediment, since the mineral nutrients available in the water limits the population size of algae)  then lead students in a discussion of possible sources of error, such as variables not kept constant between the two jars—original water’s algae count, etc. 


A Field Guide to Mud 


If you observe… It probably is… 

An orange solid on the surface or in other areas of the sediment.

Oxidized iron (Fe3+) in the sediment.  This is the same thing as rust, and can bind large amounts of phosphate (PO43-


A jet black layer in the sediment Iron sulfide (FeS).  When sulfide binds to iron, it effectively “steals” phosphate binding sites and can 

cause some phosphate to enter the water column. 


That the sediment is brown and mucky High in organic matter, or decomposed plant material.  


Bubbles coming out of the sediment Carbon dioxide and methane being produced by microbial metabolism. That the sediment smells like 

rotten eggs Sulfur gas coming out of the sediment, which a product of decomposition or microbial use of sulfate (SO42-). 


Green growth in the water or on the surface of the sediment Filamentous or single-celled algae using nutrients that are being released from the sediment for 



Stained water (tea-colored) Dissolved organic carbon (plant material that has been decomposed and broken up into to dissolved molecules).  The darker the water is, the harder the molecules that are staining the water are to decompose.  



One way to modify this lesson is in the way you lead the discussion with students.  Novice students will require help recognizing the mere existence of microscopic and atomic-scale components and may be able to only recognize that those factors are involved in some invisible processes within the algal cells. As students progress in their reasoning skills, the specific names of the matter involved and underlying processes as well as explaining how they work together can be expected. 


Other ways you could use this basic set of materials to do guided inquiry lessons with different treatments

Try the treatment “shaken vs. non shaken”  to mimic a sediment re-suspension event (wind, current, bioturbation by fish or other animals) 

Another treatment could be “dark vs. light” to display what happens with and without the possibility of photosynthesis. 

Vary the temperatures that the jars are kept at to show seasonal differences in metabolic rates 

Oxygen (use an aquarium bubbler) vs. no oxygen to display the differences in activity at the top and bottom layers of a lake 

Water from different places or sediment from different places to describe how varied aquatic ecosystems can be 

Dry vs. wet (keep one flooded, let one dry out) to show changes in ephemeral aquatic ecosystems 






1. What makes up the pond water? 





2. What makes up the sediment at the bottom of the pond? 





3. Describe some possible interactions that could occur between the things in the pond water and the sediment at 

the bottom of the pond. 







Experimental Set Up: 


Draw and label the set up as it was done in class 






What part of the set up is the control group?  __________________________________________ 


What part of the set up is the treatment group? ________________________________________ 


What differences do you expect to see in the treatment group and control group in about a week? 





Why do you think those differences might occur? 





Hypothesis statement: ___________________________________________________________ 




Data Collection 


Qualitative Observations









Quantitative Observations 














Was your hypothesis supported by the data?   









Explain what observations led you to this conclusion. 








Describe the science behind what happened in the jars.