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Lotic Environment Lesson Plans

Rick Rule and Beth-Ann Shepley
1991 Woodrow Wilson Biology Institute


OBJECTIVES

This activity will permit students to
  1. test and experiment with a natural environment inside the classroom.
  2. control and test the effect of an environmental factor associated with humans on a natural ecosystem.
  3. design and carry out a long-term experiment in which they must identify and control variables.
  4. research and propose solutions to the problems that arise when a natural ecosystem is affected by human factors.

BACKGROUND

Freshwater ecosystems are divided into two groups, lentic or standing water habitats, and lotic or running water habitats. Lentic systems are easy to demonstrate in the classroom by using a simple aquarium set-up. Lotic systems are more difficult to demonstrate due to the constant current requirement.

A classroom "river" can be constructed simply by maintaining a current of water through a common rain gutter. The set-up is quite simple, and, with a little ingenuity, the stream can be located almost anywhere. With such an arrangement, each day is unique since there are constant changes in the plant and animal populations, the water chemistry, and physical properties of the river.

One of the purposes of this model is to allow a class the opportunity to compare an artificially prepared river model to a naturally occurring lotic ecosystem. The artificial system may also serve as a model for a naturally occurring ecosystem that may be difficult for the class to travel to on a regular basis. In either case, this model permits the manipulation of abiotic factors in ways that could not be accomplished in a natural ecosystem.

Please refer to previous module, "Establishing an Ecological Baseline", that explains how to take measurements at a naturally occurring stream and river. This module explains, in detail, how data can be collected.

MATERIALS

(Found at local hardware or home builder supplies)
  • Rain gutter(10 feet long;optional number of strips)
  • outside gutter end cap
  • gutter corner
  • gutter drop outlet
  • down spout coupler (ca. $25)
  • silicon seal($3)
  • submergible pump (size dependent on size of river - $80)
  • reservoir (aquarium, trash can, or other receptacle)
  • 1" x 6" x" ? wooden board ($5) or appropriate PVC pipe ($20)
  • optional fluorescent light ($15)
  • water testing kit(Hach or LaMotte testing kit)

EXPERIMENTAL DESIGN

Teacher Directions:(For setting up and constructing original river)
  1. Length: Use the classroom space available to you. The river can be placed either vertically or horizontally. Gutter sections can be cut using any fine toothed saw(hacksaw). Rough edges should be sanded off before sealing. As pieces are cut, snap them into position according to your layout plan. (See Fig. 1 for vertical mount).


    figure 1


  2. Height: The height of each section should be different. The first section should have the greatest drop off in height. If you have the river drop more than 24 inches in height, the ends of the rain gutter will not snap together well and the corners will not seal well. The last section works best when there is no drop off and it is level. With the last section you must decide how to terminate the stream section. Here are two possibilities:

    1. The best solution is to have the out-flow close to the middle of the last section. This allows you to have a "back-water" section to the river. A midsection return requires an inverted downspout coupler and the need to cut the last section in half so the coupler will fit into the bottom of the rain gutter. Each half of the rain gutter will snap together with the downspout coupler.(see Fig. 2 & 3)


      figure 2


      figure 3


    2. The second method is easier, though you will lose the "backwater". With this method you simply cut a notch in the end cap allowing the water to drain into the reservoir. The water reentering the reservoir does create a noise problem. However, by attaching rubber tubing just below the notch, the dripping sound will be reduced considerably (see Fig. 4 & 5)


      figure 4


      figure 5


  3. Support: The river will need to be supported on the sides and ends. Side supports should be placed at three foot intervals. Materials that work well are 1" x 6" wooden board (pine works well). This can be replaced by PVC pipe which makes the river portable, but supplies less support (see Figs 6 &7).


    figure 6

    Figure 6

    figure 7


  4. Substrate: Many characteristics of a river are determined by the substrate over which the river flows. There are a number of substrates that may be used. If possible, it is best to take a natural substrate from a local river or stream. If this is not possible, use a sample of sand and gravel. The gravel portion should be of various sizes, ranging from small pea-sized gravel to large 3" and 4" stones.

  5. Seeding: Seeding the river with organisms is the key portion of this project. All that is needed is a five gallon bucket and water that can be gathered from a pond, lake, or stream.

    1. Samples are collected by removing quantities of pond weed and then shaking them vigorously in a bucket filled with stream or pond water. Be sure to make collections from the pond or stream bottom as well.

    2. Pour two-thirds of the bucket into the "headwaters" of the stream, and the remaining contents into the reservoir. Be sure to place plant materials in both the reservoir and the river.

    3. If this ecosystem is not meant to mimic a naturally occurring local river, the model river may be seeded with purchased or raised cultures of micro-organisms. Approximately one container meant for a class of 50 students (e.g., mixed protozoa) will seed the river for one year.

  6. Energy Source : In order for any ecosystem to function, it needs a source of energy. Here are three possibilities:

    1. Fluorescent light- The number and size of your lights is determined by the size of your stream. As an example, ten foot sections would require two four-foot double fluorescent units placed 12 to 18 inches above the stream. Lights should be on for 14 to 18 hours per day. A typical Gro-Lite (or two) will work.

    2. Sunlight greenhouse-Place river in the greenhouse.

    3. Sunlight windows-A southern exposure should work the best. Fluorescent light can be added if needed to supplement on dark days.

  7. Reservoir: The reservoir should be able to hold at least 20 gallons of water. A large plastic garbage can or an aquarium work well.

  8. Maintenance: The river does not require a lot of care, however, each day you should check the water level in the reservoir. If it is too low, fill with more pond or river water. Occasionally check the pump, filter, and aquarium hose. At the end of the year, you need to scrub the entire system with an algacide to start anew without excessive algae growth. After using the algacide, rinse the system well.

Teacher Directions

(for river ecosystem study)
  1. Many different abiotic parameters of the ecosystem can be tested using the river. Some of the chemical parameters that have been tested previously include:
    • pH
    • dissolved oxygen
    • phosphates
    • nitrogen-containing compounds
    • water hardness
    • trace elements (iron, copper, zinc)
    • carbon dioxide

    Other abiotic factors that can be measured include:

    • temperature
    • current velocity
    • substrate particle size + substrate content
    • light intensity

  2. The river is also used to measure organisms. These can include both microscopic and macroscopic organisms.

  3. Although one of the benefits of this exercise is that it can be used to demonstrate a plethora of ecological principles, the following example is provided as a simple model of what might be accomplished.

    Two days. The class is divided into small groups and each is assigned one abiotic factor to be responsible for. Each group is given specific instructions for their abiotic factor. For ease of data collection, the river is divided into the same number of sections as there are groups. Groups test each section of the river for their assigned abiotic factor and collect data.

    Three days. (This time frame is dependent upon students skill with microscopes). Each group is assigned one section of the river. Students take water samples from their section of the river and identify and count the micro- and macro-organisms present. This data is recorded.

    Once a month during remaining portion of Semester One. Same groups will continue to collect and compile abiotic and biotic data.

    Four days. Baseline data is compiled. Students graph the compiled data so that relationships can be seen between the numbers of organisms and abiotic factors. The class formulates hypotheses to account for any relationships observed. One hypothesis, dealing with one factor (i.e., "Thermal pollution causes the number of microorganisms to increase.) is selected for testing. Class designs experiment that will allow that factor to be tested and that abiotic factor is changed (i.e., heater is added to the reservoir and adjusted to meet class specifications for temperature).

    Once a month for remainder of year. Groups will continue to collect and compile abiotic and biotic data.

    Three days at end of year. Experimental data is compiled. Students graph the experimental data and determine if the hypothesis is supported or disproved. Other areas for discussion include:
    • -sources of error
    • -statistical analysis of data
    • -further experimental lines of inquiry
    • -solutions to river problems caused by humans

  4. Further extensions of this lab are:
    • To compare a naturally occurring stream or river in your with the artificial river in your classroom where the variables can be controlled.
    • To compare standing water with running water by using the "backwater" section and comparing with the rest of the river
    • To use the river as a means of integrating the sciences; looking at the physics of liquids and kinematics, looking at it as a sophisticated stream table for earth science; looking at it as a constant source of chemical experiments from a natural environment. .
    • To use the river as the basis for studying the affects of pollutants on a closed ecosystem.

  5. Ways to use the system for classes with different academic objectives:
    • Self-designed long term experiments
    • Different techniques for identifying organisms
    • Testing different number of abiotic and biotic variables that the class monitors.
    • Amount of group research into pollutants and the river system carried out by students themselves.
    • Sophistication of statistical analysis of data.

RESOURCES

BOOKS:

Andrews, William A. Freshwater Ecology. 1972.

Andrews, William A. Environmental Pollution. 1972.

BSCS. Interaction of Ideas and Experiments. Prentice-Hall. 1983:327-329.

Kimmel, William G. and Moon, Thomas C. An Introduction to Water Pollution Biology: Theory and Practice. Hach Company. 1982.

Smith, Robert Leo. Ecology and Field Biology. 4th ed. NY: Harper and Row. 1990.

SUPPLIERS OF ORGANISMS FOR ADDITIONAL SEEDING:

Carolina Biological Supply
2700 York Road
Burlington, North Carolina 27215

Wards Natural Science
5100 West Henrietta Road
P.O. Box 92912
Rochester, New York 14692-9012

Sargent-Welch
7350 N. Linder Ave
P.O. Box 1026
Skokie, Illinois 60076-1026

Connecticut Valley Biological Company
82 Valley Rd.
P.O. Box 326
Southhampton, MA 01073


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