Circulation of Water in Addition to CO ₂ , O ₂ and Plant Biomass in an Artificial Ecosystem Comprised of Humans, Goats and Crops During Three 2-Weeks Closed Habitation Experiments Using CEEF 2007-01-3091

The Closed Ecology Experiment Facilities (CEEF) were installed to collect data for realistic estimation of radiocarbon transfer in the ecosystem. Two-week experiments were conducted three times from September to November of 2006, in which two human subjects called as eco-nauts were enclosed and worked in an airtight facility, the CEEF. The eco-nauts were changed after a week from beginning of each experiment. In these experiments, a Plant Module (PM) with 23 crops, including rice, soybean, peanut, and sugar beet, was connected to an Animal & Habitation Module (AHM) which included the eco-nauts and two goats. 91.8-94.6% (by weight) of the food consumed by the eco-nauts and 79% of the feed to the goats (straw, leaf and bran of rice, leaf and stem of soybean, and leaf, stem and shell of peanut) were produced from crops in the PM. Amount of oxygen produced by the crops was more than the amount consumed by respiration of human and animals in these experiments. The oxygen added to the atmosphere of the PM by photosynthesis of crops was separated and supplied to the atmosphere of the AHM. Increased carbon dioxide in the AHM atmosphere by respiration of eco-nauts and goats was separated and supplied back to atmosphere of the PM. Almost carbon in the waste was withdrawn and not recycled in these experiments. Therefore, extra carbon dioxide was added to the PM atmosphere in order to compensate for the demand from photosynthesis of the crops. In addition to carbon dioxide, oxygen and plant biomass, water was also circulated in the CEEF in 2006, for the first time. Average water amounts of input to and output from the PM were 2090 L d⁻¹ and 2080 L d⁻¹, respectively. The difference between them was less than 0.5% of the input, and was comparable to the amount of water with harvested crops. Average amount of water of input to and output from the AHM were 75.2 L d⁻¹ and 68.2 L d⁻¹, respectively. Urine of the eco-nauts (1.7 L d⁻¹) was withdrawn. Considerable water might be withdrawn as steam by pyrolysis of feces and urine of goats. These may account for the difference between the input and the output of water for the AHM. In the 2005 experiment, 46500 L of waste nutrient solution was withdrawn for 27 weeks of a whole growing period including 10 weeks of harvesting period. In the 2006 experiment, only 500 L of that was withdrawn during 38 weeks including 18 weeks of harvesting period. However, harvested edible biomass of almost crops in 2006 was less than that in 2005. It is considered that usage of newly made nutrient solution only during seedling growth period could improve final biomass production considerably.