THE URBAN ECOSYSTEM- Secondary
Introduction:
Select a study area on your school campus, nearby vacant lot, or park. If possible, the area should contain some "volunteer plants" (weeds) and bare ground, as well as paving and/or lawn.
Introduction:
Materials: (for each group)
Urban Safari Tasks:
A. Microclimates
Air Temperature
Make a sketch of your study area indicating the green areas, paving, and buildings on a grid representing aquare meters. Make several temperature readings 1 meter above the surface and record your data in oCelsius on the map where you made the reading. Be sure to make readings above any of the following, if found in your study area:
Look for areas on your map that have the same temperature. Connect these areas with a curved line on your grid map to show areas of "isotherms".
How do your readings compare over the grid map? Is there any pattern?
What effect do plants have on the microclimate?
What effect do the built structures ( streets, sidewalks, buildings) have on the microclimate?
Cities are sometimes characterized as "urban heat islands". Why do you think that might be?
Relative humidity is the water vapor in the air at a given temperature compared with the maximum amount of water vapor that the air could hold at that temperature. It is a ratio expressed as a percentage. The relative humidity can be measured by comparing a wet bulb thermometer reading with a dry bulb thermometer reading. Read the instruction sheet with the sling psychometer and determine the relative humidity in the following places of your study area.
What is here? What do we see in the urban environment that we can recognize as an ecosystem? If we look closely enough, we will discover living and non-living systems that may not be the same as before man's impact on the area, but still basically interact like natural ecosystems. For example, a city bird may nest on a street sign rather than a tree and eat worms found in exotic fruit trees, but it still seeks a place to live and exchanges materials with the environment.
PART I: THE ABIOTIC PART OF THE ECOSYSTEM- Work in small groups.
An ecosystem is comprised not only of living things, the biotic part of an environment, but also of the physical environment, the abiotic part of the environment. Some of the abiotic factors include the water, air, weather, and geological features found in a given area.
meter stick or tape measure
petroleum jelly (vaseline)
soup can/soil sampling tube
sling psychrometer
ozone badges
thermometers
index cards
string
pH paper
magnifier
open barren ground or soil:
open concrete, asphalt, or cement:
open grass or weeds:
open shrubbery:
open puddle, pool or pond:
under the shade of a tree:
shade of a building:
Relative Humidity
| dry bulb oC | wet bulb oC | rel. humidity | |
| open barren ground: | ________ | ________ | ________ |
| open grassy area: | ________ | ________ | ________ |
| open puddle or pond: | ________ | ________ | ________ |
| under the shade of a tree: | ________ | ________ | ________ |
What is the relationship between the air (dry bulb) temperature and the relative humidity? What differences in temperature and relative humidity would an insect crawling on the ground experience compared to one flying 3 meters in the air? How do plants affect the amount of moisture in the air? Why? How does standing or moving water affect the amount of moisture in the air?
B. Air Quality
Option One:
Number your index cards 1-4. Spread one side of four index cards or pieces of acetate with a thin layer of petroleum jelly (clear contact paper can be used). Place cards 1 and 2 with the sticky sides up on open ground in two different places; place the others within the foliage of trees (secure with paper clip). For best results, place the cards out at the start of your study and retrieve them at the end of your study.
Compare the dust particles that have been trapped on the cards. You can use your hand lens to observe the particles.
Which card contained the least particles? Which had the most? Why? Do trees cleanse the air? How?
Option Two:
If available, wear an "ecobadge" after arriving at your study site. Use the color chart to determine the parts per million of ozone exposure for one hour of exposure (the top opening) Compare with the other sites.
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Locations: ________________ After One Hour ______________p/mil.
Health Risk of Air Quality: ________________
Do you think ozone concentrations are greater in cities or in rural areas? Why?
C. Soil
1. Litter and top soil collection: Collect samples of the litter (loose organic material on the surface of the soil) and top soil. Place these in labeled zip-lock bags to take back to the classroom.
Back in the classroom, take a pH reading of the soil in the zip-lock bags. ( if the soil is not moist, remove a teaspoonful of it and add drops of distilled water.
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_________pH of top soil.
Empty the contents of the zip-lock bags on a sheet of white paper and examine with a hand lens or dissecting scope. Note any parts of plants, insects, and other organic matter (dark). What kind of crystals and inorganic matter can you discern?
A quick way to assay the soil is to note the color of your sample. A dark or black soil is high in humus (decomposed organic matter). A light color denotes sand. The color of clay is in between.
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_________color of soil.
Weigh a small sample of soil from your bag.
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_________weight of soil in g.
Let your soil sample dry over several days (can be dried in an oven) and reweigh the contents of the sample.
|
Original weight of soil |
x 100 = percent moisture in soil |
Weigh a small sample of your dried soil and place in a crucible. Heat over a bunsen burner until the humus turns to ash. Weigh again.
|
Original weight of dry soil |
x 100 = percent humus in soil |
2. Core sample:
Option one-Use a soup can with two open ends. Twist one open end into soft soil. Dig the soil away from one side and slip a piece of cardboard underneath. Wrap the ends of the can securely with aluminum foil and rubber bands.
Option two - Use a soil sampling tube.
Remove the soil in the sampling tube or soup can carefully by pushing a stick or plunger into the opposite end. It is okay if the soil core doesn't hold together. Drag the contents of the soil across a sheet of white paper so that the layers of soil, if any, are still separated. Examine with a hand lens. How many different layers can you observe? How does each differ from the other in color, particle size, components, etc.? Draw a profile of your core to show the various layers.
Add your soil sample to a tall container of water. Shake vigorously and let settle. Note the comparative thickness of each layer and its percentage of the total sample.
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____________% clay ___________% silt ___________% sand
 |
 |
 |
 |
Refer to the composition charts above. What is the soil type or combination type of your sample?
PART II: THE BIOTIC PART OF THE ECOSYSTEM
| Materials: (For each group) | |
|---|---|
|
Hand lens
Sketching paper (optional) Lengths of string (5 or 10 meters) Clipboard (or small notepad) and pencil Binoculars (optional) |
Camera (preferably a Polaroid)
Bread crumbs, sugar, cracker pieces Tape recorder (optional) Bug box Reference books Stakes |
Urban Safari Tasks
A. Plants
1. Study a plot or quadrant within the same area that was used in the abiotic study. The plot can be "staked out" using string and stakes or delineated with rocks and pebbles. If the area contains trees, the plot or quadrant can be as large as 100 square meters. If there are no trees, the quadrant can be as small as 1-9 meters.
Sketch a quadrant map and record the location and number of plants using symbols. For example, Δ could symbolize trees and * could symbolize shrubs. It is not necessary to know the names of each and every plant, but you could use the identification guides to help identify them.
Are any of the plants found in every part of the quadrant? Are some clustered in particular parts? Why do you think there may be clusters of plants?
Are there areas bare of plants? How would you explain this?
Relate the plants to the temperature and relative humidity map you constructed in part A.
Would you predict that the plants found in your quadrant stay the same or change markedly during different parts of the year? Is there any evidence from your field work to support this?
2. Collect 5 different kinds of leaves. Observe the color, leaf edge, veination, cuticle and its covering, size, thickness, and shape. Indicate leaf characteristics that would help a plant adapt to arid conditions and how they do.
Which plants are growing wild and which are planted by people? Do you see any plants growing on man-made structures? Do you see any evidence of foot traffic impacting the plant growth?
B. Animals
Observe at ground level, eye level and overhead in the same quadrant used above. Record your findings on your quadrant map and clip board and with your Polaroid camera.
Look for signs of animals: tracks, homes, evidence of eating, fecal deposits, pathways. What do these signs tell you about who lives here?
Look for signs of who eats whom/what. Try to determine the food chain in which this animal exists. Do the animals you have discovered live off of nature or human intrusions (garbage, gardens, pet food, etc.)?
Do you see any animal homes in human-built structures?
Be a bird-watcher: Where do you see them? What do they seem to be doing? What do they look like (color, shape)? Can you identify any of them? (Common city birds are crows, sparrows, finches, mockingbirds, jays, starlings, pigeons.) How many of each species do you see?
Compare the "wildlife" to human-influenced life: Are there any wild animals? Are there any domestic animals?
Be an ant-watcher: Where do you see them? What are they doing? Do you observe any division of labor going on? Can you influence their behavior by scattering food particles?
What do you see that is reflective of human impact? Do you see any harms or benefits from that impact?
Pick one animal at your level to examine as thoroughly as you can. If it is an insect, you can put it in the bug box, but be sure to put it back when you are finished observing it. Sketch or photograph it. Why did you pick this item?
Use your sense of smell. What is the dominant smell in the area? What is it caused by? Is it natural or man-made?
Close your eyes. Listen to the sounds around you. Which one do you notice most? Why? Is it a sound from nature, or man's creation? If you have a tape recorder, record for a while. Play it back and see if what you focused on was what the tape recorder picked up.
Wrap-up:
When you are finished with your safari, discuss your findings with the other members of your group. Discuss with your group how the abiotic environment determines and affects the living things found in your area. Discuss how living things affect the abiotic environment. Chart the discussion on chart paper.
Then share your group findings on chart paper with the other groups when you return. Compare what you found with their experiences, noting similarities and differences. Share any photographs and or tape recordings you made also.