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Using Benthic MacroInvertebrate Assemblages as
   Indicators of Water Quality and Stream Health


WOODROW WILSON ESI '98                                       SAINT JOHNSBURY ACADEMY
Don Gibbs       9-12 Bio/Chem/Physics Instructor                         PO Box 960    7 Main Street               dgibbstj@pop.k12.vt.us                                                        Saint Johnsbury, Vermont   05819   

 
It is sometimes difficult for students to address questions of environmental disturbance from a biological perspective.  In river studies that propose to describe the health of a system, no thought, beyond searching for dead fish, is ever given by the students to the biology of the place or assemblage of plants and animals that comprise that community.  For the vast majority of students, it is the abiotic factors that immediately come to mind.  Biology students initially latch on to strategies that would call upon the tools of chemistry and physics to answer the question and frame the study (e.g. measure the amount of toxins in the water, sediment, and organisms; examine and monitor erosion rates or stream flow characteristics, dissolved oxygen concentration, pH and so on).   When we turn the conversation toward biology, they offer suggestions that presuppose a strong understanding of specific areas of life science such as pathology (e.g. dissect the organisms and search for evidence of disease).  The question needed to be refined so that my 9th grade students could access it, comprehend it, and manipulate it within an experimental and biological context.

    Focusing Question:

    Primary VT Standard Addressed:                 Analyze and explain natural resource management and demonstrate an understanding of ecological interactions and
                interdependence between humans and their resource demands on environmental systems.
 
What are BMI?
    The term "benthic" means bottom dwelling. Benthic invertebrates lack backbones and either live in, crawl upon,
or attach themselves to the bottom (substrate). The term "macroinvertebrates" refers to invertebrates easily seen with the naked eye.  Most benthic macroinvertebrates found in flowing water are aquatic insects or the juvenile stages of many insects that we know, and fear, as flying adults. Other benthic macroinvertebrates include other arthropods, worms, and clams.
    Benthic macroinvertebrates often go unnoticed because of their size and habitat, but they are an extremely important part
of river ecosystems. Collecting benthic macroinvertebrates is a relatively easy process and the computationally simple measures of taxa richness, density, and % composition can produce an understanding of a river's condition.  Such statistics are useful because benthic organisms have several characteristics that make them reliable indicators of water quality. In particular, they are sensitive to physical and chemical changes to their habitat and live in the water for the entire aquatic stage of their life cycle.   Additionally, because benthic organisms cannot easily escape by swimming away, as some fish can, we can be certain that samples reflect local conditions. Thus, by sampling BMI and analyzing population parameters, students are truly developing a picture of site specific conditions that have persisted in the water over a period of time.

Making the Experiment Accessible to Students
    What I find so appealing about this kind of study is that it incorporates experimental design, the establishment of standardized procedures, field work, the classification of specimens, data analysis and interpretation, all within an atmosphere of environmental stewardship.  Although the River Watch Network's Guide to Benthic Macro Invertebrate Sampling gives details concerning the methods and analysis, it does little to get the ball rolling in your classroom.  Some tips, then, to implementing this kind of work in your classroom:

    This year I will use CBL sampling techniques to supplement the biological information my 9th graders receive.  Because I also teach chemistry, I will ask those students to carryout the chemical aspects of this study.  In this way, juniors and freshmen will come together to present information, discuss the implications, refinements and supplemental project ideas.  My science department at Saint Johnsbury Academy has also introduced a capstone science requirement that affords students at each grade level the opportunity to author and publish an original study.  I see this River Watch experience as a way to reinforce the scientific method, give students guided and practical experience in experimental design and provide them a possible springboard for their capstone project.

 Possible Student Directed Projects



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