Simulation of community metabolism and atmospheric carbon dioxide and oxygen concentrations in Biosphere 2

Abstract

The complexity and scale of Biosphere 2 under materially closed conditions represented a unique opportunity to investigate couplings between elemental cycles and community metabolism. For this paper, simulation models were developed to explore individual biome effects on atmospheric composition and carbon cycling inside the enclosure. Results suggest soil respiration rates, light intensity, and acid–base equilibrium control atmospheric carbon dioxide and oxygen under materially closed conditions. Experiments with the overall Combined Biome model indicate: (1) the agriculture biome has a greater effect on atmospheric composition than the other biomes due to its large area, high net productivity, and biomass harvests; (2) the rainforest, which occupies ≈20% of Biosphere 2 area, may be responsible for 50% of total community production and respiration of oxygen; (3) the savannah and wetland biomes may be sources of carbon dioxide in the long term; (4) the ocean biome has less effect on atmospheric composition than the terrestrial biomes; and (5) the desert biome may lower carbon dioxide in the atmosphere as much as 2000 ppm during low light. Diurnal curve analyses of oxygen and carbon dioxide from early 1995 produced an average community gross production rate of 23 g O 2/m 2 per day, a community respiration rate of 25 g O 2/m 2 per day, and an average carbon dioxide absorption rate of 0.2 g CO 2/m 2 per h.