A. Alling

Living off the land: resource efficiency of wetland wastewater treatment.

Bioregenerative life support technologies for space application are advantageous if they can be constructed using locally available materials, and rely on renewable energy resources, lessening the need for launch and resupply of materials. These same characteristics are desirable in the global Earth environment because such technologies are more affordable by developing countries, and are more sustainable long-term since they utilize less non-renewable, imported resources. Subsurface flow wetlands (wastewater gardens(TM)) were developed and evaluated for wastewater recycling along the coast of Yucatan. Emergy evaluations, a measure of the environmental and human economic resource utilization, showed that compared to conventional sewage treatment, wetland wastewater treatment systems use far less imported and purchased materials. Wetland systems are also less energy-dependent, lessening dependence on electrical infrastructure, and require simpler maintenance since the system largely relies on the ecological action of microbes and plants for their efficacy. Detailed emergy evaluations showed that wetland systems use only about 15% the purchased emergy of conventional sewage systems, and that renewable resources contribute 60% of total emergy used (excluding the sewage itself) compared to less than 1% use of renewable resources in the high-tech systems. Applied on a larger scale for development in third world countries, wetland systems would require the electrical energy of conventional sewage treatment (package plants), and save of total capital and operating expenses over a 20-year timeframe. In addition, there are numerous secondary benefits from wetland systems including fiber/fodder/food from the wetland plants, creation of ecosystems of high biodiversity with animal habitat value, and aesthestic/landscape enhancement of the community. Wetland wastewater treatment is an exemplar of ecological engineering in that it creates an interface ecosystem to handle byproducts of the human economy, maximizing performance of the both the natural economy and natural ecosystems. Wetland systems accomplish this with far greater resource economy than other sewage treatment approaches, and thus offer benefits for both space and Earth applications.

INITIAL EXPERIMENTAL RESULTS FROM THE LABORATORY BIOSPHERE CLOSED ECOLOGICAL SYSTEM FACILITY

An initial experiment in the Laboratory Biosphere facility, Santa Fe, New Mexico, was conducted May-August 2002 using a soil-based system with light levels (at 12 h per day) of 58-mol m-2 d-1. The crop tested was soybean, cultivar Hoyt, which produced an aboveground biomass of 2510 grams. Dynamics of a number of trace gases showed that methane, nitrous oxide, carbon monoxide, and hydrogen gas had initial increases that were substantially reduced in concentration by the end of the experiment. Methane was reduced from 209 ppm to 11 ppm, and nitrous oxide from 5 ppm to 1.4 ppm in the last 40 days of the closure experiment. Ethylene was at elevated levels compared to ambient during the flowering/fruiting phase of the crop. Soil respiration from the 5.37 m2 (1.46 m3) soil component was estimated at 23.4 ppm h-1 or 1.28 g CO2 h-1 or 5.7 g CO2 m-2 d-1. Phytorespiration peaked near the time of fruiting at about 160 ppm h-1. At the height of plant growth, photosynthesis CO2 draw down was as high as 3950 ppm d-1, and averaged 265 ppm h-1 (whole day averages) during lighted hours with a range of 156-390 ppm h-1. During this period, the chamber required injections of CO2 to continue plant growth. Oxygen levels rose along with the injections of carbon dioxide. Upon several occasions, CO2 was allowed to be drawn down to severely limiting levels, bottoming at around 150 ppm. A strong positive correlation (about 0.05 ppm h-1 ppm-1 with r2 about 0.9 for the range 1000-5000 ppm) was observed between atmospheric CO2 concentration and the rate of fixation up to concentrations of around 8800 ppm CO2.

Effects of a Spaceflight Environment on Heritable Changes in Wheat Gene Expression

Once it was established that the spaceflight environment was not a drastic impediment to plant growth, a remaining space biology question was whether long-term spaceflight exposure could cause changes in subsequent generations, even if they were returned to a normal Earth environment. In this study, we used a genomic approach to address this question. We tested whether changes in gene expression patterns occur in wheat plants that are several generations removed from growth in space, compared to wheat plants with no spaceflight exposure in their lineage. Wheat flown on Mir for 167 days in 1991 formed viable seeds back on Earth. These seeds were grown on the ground for three additional generations. Gene expression of fourth-generation Mir flight leaves was compared to that of the control leaves by using custom-made wheat microarrays. The data were evaluated using analysis of variance, and transcript abundance of each gene was contrasted among samples with t-tests. After corrections were made for multiple tests, none of the wheat genes represented on the microarrays showed a statistically significant difference in expression between wheat that has spaceflight exposure in their lineage and plants with no spaceflight exposure. This suggests that exposure to the spaceflight environment in low Earth orbit space stations does not cause significant, heritable changes in gene expression patterns in plants.