Engineering of Biosphere 2: closure and energy

As an experimental apparatus, Biosphere 2 was predicated on material closure to permit investigation of ecological processes without unknown sources or sinks outside the ecosystems under study. The atmospheric leak rate is demonstrated to be less than 10% per year. The enabling technology to achieve the low leak rate is expansion chambers called "lungs." Closure enables use of mass balance equations to track chemical pathways (e.g., of carbon dioxide and oxygen). Energy and information pass across the enclosure without incurring any material transfer. Water is fully recycled.