Biospheres
Last update: August 29, 2007
Biospheres (or ecospheres) are small, mostly closed ecosystems containing
a mix of plants and animals that meet each other's needs to sustain life. The
only input to a biosphere is energy (light), all other materials are sealed
within it and recycled through the process of life, death, and decay. Earth is
a biosphere, albiet on a much grander scale than the small systems presented here.
In a typical small hobbyist system, a plant such as algae is grown, which provides
food for a few small animals, such as brine shrimp. The shrimp excrete waste, which
is broken down by bacteria into a form that the algae can then use and the cycle
repeats. The shrimp consume oxygen and generate CO2, which the algae absorbs. The
algae produces more oxygen. The whole system is enclosed in a sealed vessle which
is transparent to admit light and allow observation. Since all the mass in the system
is fixed, the trick in building a biosphere is to adjust the amount of plants, animals,
and buffer space (water, air) such that everything is in balance. If anything is out of
whack the system may crash (all oxygen consumed, toxic levels of CO2 and/or other
waste products build up, etc) and the lifeforms within perish.
Building a biosphere is an interesting experiment into symbiotic systems. Unlike
aquaponics, which uses the earth's atmosphere to supply
oxygen and remove CO2, a biosphere can support a far smaller animal to plant ratio.
Biospheres have been built in everything from old beer bottles to giant building complexes,
such as Biosphere II. Many amateurs have had good luck using food-grade plastic
containers, such as 2 liter soda bottles or storage jars with tight seals, although with
some work an old aquarium could be sealed for this purpose. Various types of algae can
be grown or collected, and many have had good luck with brine shrimp or "Sea Monkeys"
(brine shrimp bread to grow slightly larger than the standard type). Food available
from pet stores is typically powdered algae which can be cultured for use in a
biosphere (this is typically included with "Sea Monkeys" when you buy the kit).
The proper amount of light must be used with a biosphere. Direct sunlight will usually
heat the container contents to lethal levels quickly, and even too much indirect
light will cause algae blooms and subsequent shifts in water pH, which can also cause
disaster.
More specific information is available at the links below, especially the
Yahoo group.
For my first experiment, I took the advice of
Robin Ohm
and collected samples of water from a small stream. This water was placed into
two quart-sized glass canning jars with metal lids:
The jar on the left contains a mix of stream water and dechlorinated tap water. The
center has 100% stream water. The jar on the right contains water taken from a
northern Minnesota lake collected at a later date.
After sealing, the jars were placed under three flourescent light units running on a
timer (16 hours on, 8 hours off), in an area with an average temperature of about 75F.
The jars were clear at first, but the 100% stream water jar started growing a layer
of green algae after about a week. A number of tiny, fast-swimming animals were
also visible (I'll try to get photos when a new macro lens arrives for my camera).
At the 10-day point, the 100% jar algae has turned
mostly brown and is producing bubbles:
Some strand-like algae is also growing, and the micro-swimmers are still zipping around.
The dilute stream water jar also contains swimmers, but the algae is still all green:
Could this be due to lower nitrate levels in the diluted water, not causing an overgrowth
of algae? Time will tell.
Links: