Biospheres are self-contained ecosystems that support plants and animals. Biospheres may be terrestrial, freshwater, combination terrestrial/freshwater, or marine. Although it may take a few tries and a bit of adjustment, in terms of the number and type of organisms, to create a balanced biosphere, the final result will be a self-sustaining system. Biospheres enhance the aesthetic of a child's room or classroom, provide hours of entertainment, and promote scientific thought. You can create your own simple bottle biosphere in a single afternoon with only a few basic materials found in your home or collected from nearby wooded areas and ponds or streams.
Rinse the 2-liter bottles thoroughly and remove labels. Remove any non-transparent stabilizer pieces from the bottom of the bottles. Replace the bottle caps and screw them on tightly.
Cut around the top of one of the bottles approximately one inch down the straight sides below the neck to create a funnel-like biosphere cap and an aquatic reservoir.
Cut around the bottom of one bottle approximately one inch up the straight sides of the bottle below the fluted base to create a terrestrial chamber. Discard the bottom piece of the bottle.
Drill a hole through the center of the bottle cap on the terrestrial chamber. The hole should be slightly larger than the diameter of your cotton string.
Add pond or stream sand to the bottom of the aquatic reservoir. Also add pond or stream water to the aquatic reservoir to a depth of approximately six inches.
Add a few algae-eating, aquatic organisms, such as snails or tiny fish, and aquatic plants to the aquatic reservoir.
Cut a piece of cotton string two feet long and tie a knot in the middle. Soak the string in pond or stream water until fully saturated--approximately ten to fifteen minutes. Thread the string through the hole in the bottle cap on the terrestrial chamber so that the knot is in the bottle cap.
Rinse gravel thoroughly with tap water. Invert the terrestrial chamber and add a layer of rinsed gravel two inches deep. Be sure you don't bury the cotton string. Coil the cotton string in a spiral around the chamber over the gravel.
Add several inches of moist forest soil to the terrestrial chamber. Add a small amount of pond water to the soil if necessary. Plant a small shade-tolerant plant in the soil of the terrestrial chamber. Cover the surface of the soil with leaf litter containing small invertebrate organisms, such as springtails and pillbugs.
Place the terrestrial chamber into the aquatic reservoir. The bottle cap should be above the level of the water. Remove a small amount of water if necessary. The cotton string should hang into the aquatic reservoir--it will act as a wick to provide water to the terrestrial chamber.
Add twigs or other ornamental objects to the terrestrial chamber for visual interest. Place the funnel-like biosphere cap over the top of the terrestrial chamber and place the finished biosphere in a sunny location.
Hang your bottle in a window for easy viewing and access to sunlight.
Add a few limestone rocks, such as calcium rocks from an aquarium supply store, to the water to help adjust the pH.
Add a small amount (e.g., 1 tbsp.) of pond scum to the water to kick-start algae growth.
Don't add too many snails to your ecosphere or they will eat all of the algae. Start with one snail and add more later if needed.