We believe that ample water and nutrients, mixed with the short lived, annual lifestyle of H. incana, led these plants to produce greater above ground biomass as compared to naturalized, or wild, H. incana found at the field sites. Conversely, native E. fasciculatum specimens showed more below ground root material than that of the invasive species. This is due to the perennial habit of the native, where a taproot and established root system would be necessary for survival. Because perennials such as E. fascicultum do not respond as quickly to increased nutrient availability, the species would not develop the same amount of biomass as that of H. incana during the exposure period. Overall, we observed complex movements of tracer within the individual PLS systems which may explain why we computed substantially different N deposition rates using sub-components of the modules than we computed with the module-average approach.Since Deployment 3 had aluminum foil installed 2 weeks after the exposure had begun, some nitrogen may have been lost to algal or microbial biofilms. In a few Hoagland Controls, there were also very small weeds that were also present. The small seedlings were included in the module calculations as they utilized module nitrogen during exposure, possibly adding a small source of error to deposition rates. Additionally, the prolonged time to senescence, 130 days, might have lowered the apparent N deposition rate as the winter season is not a time in which H. incana readily grows; instead H. incana sprouts with the last spring rains and grows primarily in the summer season. Because H. incana was grown out of season, we speculate that the plants were transpiring less water and therefore assimilating less gaseous N than plants exposed during the summer deployments , and therefore growing much slower. This is confirmed by the fact that Deployment 3 took 130 days for H. incana to reach senescence,growing raspberries in container but in Deployments 1 and 2 the species took approximately 70 days to senescence. I also noted that invasive treatments seemed to have smaller above ground plant structures than in previous deployments.

The AP 15N of below ground biomass had a relatively narrow compared to that of the above ground plant material . While this might be a physiological artifact, we speculate that nitrogen settling on the above ground plant surface directly from the atmosphere may have contributed to greater isotopic dilution and variability in the above ground biomass. Since below ground plant material is not exposed to direct nitrogen deposition, the roots did not experience the same depletion of the 15N tracer. In contrast, stomatal uptake of atmospheric N, and the subsequent allocation of this N to the root system, would be the major pathway in which root tissues would become depleted of 15N. The Control treatments, lacking a plant component but containing all other ITNI parts, resembled a passive nitrogen deposition collector, because there was no plant component in which to actively uptake gaseous nitrogen or deposition. Modules with plants had higher apparent N deposition because of active absorption of atmospheric N through leaf stomates and because of the larger surface area of plant canopies relative to the sand surface in the Control modules.In all deployments, and across all treatments, ITNI modules exhibited the following pattern of depositions rates using the different computation methods: Module Average> Plant> Above ground. This finding is explained by two factors. First, the plant is more isotopically enriched than the liquid and sand components of the ITNI modules so that the portion of Equation 1.3 in parentheses was lower when computed using only the plant than when it was computed using the module average; this smaller number was then multiplied by Ns to yield a smaller apparent N deposition. Secondly, the Ns value for the plant and the above ground plant are lower than the Ns for the entire module, further decreasing the value of N deposition in Equation 1.3. Thus our hope that the PLS would reach an internal isotopic equilibrium so that selecting only plant tissue for ITNI calculation could result in accurate N deposition failed. The high levels of tracer in the plant occurred because of early exponential growth when 15N tracer was abundant in the liquid reservoir. As the Deployment continued, the plant remained isotopically enriched compared to the other components of the module. The sand and liquid reservoirs, because of their small size, experienced higher levels of isotope dilution. This leaves the plant more enriched as the exposure continues as the plant does not appear to exude the 15N-labelled material back into the liquid and sand after it has been allocated to plant tissues.

Therefore, the different computational methods of Plant and Above ground are not helpful in determining the nitrogen deposition experienced by the modules. Module Averages are the only way to compute nitrogen deposition to ITNI modules. Module Average nitrogen deposition rates were greatest in Deployment 2, compared to Deployments 1 and 3, perhaps due to improved nitrogen recovery at harvest. As a consequence of calculating nitrogen deposition rate via the module average ITNI method, the rate is dependent on nitrogen recovery as represented by Ns. As Ns decreases, the nitrogen deposition rate experienced by the module also decreases, therefore underestimating true nitrogen deposition to the module over the exposure period. Since Deployments 1 and 3 lacked a foil barrier to deter algal/microbial growth in the module during the exponential growth of the plant, they recovered less nitrogen at harvest as a result. He et al., 2010, stated that plant detrital material was neglected in their ITNI measurements. In contrast, I included plant detritus during the harvest of the plants. Though the plant detritus was not actively taking up gaseous nitrogen, it derived from the ITNI plant and still experienced dry deposition to surfaces and therefore was included in the sampling for the respective modules. Plant detritus was most likely a conundrum for He et al. as the agricultural species that they utilized had plant organs that senesced during exposure. This senescence led to the volatilization of NH3, however our modules were harvested as soon as the plants senescenced, therefore reducing this nitrogen loss. In the case of E. fasciculatum treatments, there was no plant detritus to include, further supporting our suggestion that perennials, instead of agricultural or annual species, should be used as ITNI study specimens. Extrapolation methods were introduced by Russow and Bohme 2005 in which the plant density of the module was modified to match the field density of the same species. To correct for this in our own study, Bromus rubens, Hirschfeldia incana, and Eriogonum fasciculatum were sown in the ITNI modules at field density or very close to that of field density when sown a single seedling to a single module . Therefore, only the exposed sand surface was necessary for extrapolating ITNI calculations to the hectare level. Similarly to He et al. 2010, our study also experienced lower nitrogen deposition rates for species grown outside of their traditional growing season. He et al. Contributed this finding to less active uptake of gaseous nitrogen as compared to normal growing conditions. However, they found that despite this, the ITNI method produced higher deposition rates than traditional methods and concluded that this excess nitrogen deposition was active uptake by the plant.

According to the National Atmospheric Deposition Program, total nitrogen deposition for our study area ranged from 12 kg ha-1 yr -1 to 18- >20 kg ha-1 yr -1 . When extrapolated to an entire year, the ITNI method estimated total deposition to be approximately 38 ha-1 yr-1 , also exceeding NADP’s measurements. Since our study site was not dominated by wet deposition,raspberry container size as was He et al.’s, we attributed this excess deposition to the active uptake of gaseous nitrogen by the plant and improvements upon the shortcomings in dry deposition measurements in the region . Future ITNI experiments in arid and semi-arid regions should utilize a single or a very few, representative short-lived perennial species. We make this suggestion based on the considerable variability in biomass among individual specimens in the annual invasive treatments. If a short-lived perennial was used instead of an annual, we suspect there would be less influence from early senescence and less influence from a life history that promotes quick growth. Annual life history traits can increase the chance of biomass loss due to seeding events, flowering, pollen release, etc. By working with a perennial plant, ITNI operators can still grow a plant with enough aerial biomass to actively uptake nitrogen, but the plant is less likely to senesce or seed during the exposure period. Additionally, we suggest picking one, or just a few representative species, for the ITNI measurements across regions. Interspecies differences in life history, physiology, and aerial plant parts would interfere with a direct comparison across a region. However, if a single species were utilized across all habitats in question, spatial patterns in N deposition would be easier to detect. We also suggest that ITNI modules contain the same improvements as I have noted, such as the addition of a mechanism to prevent herbivory bird visitation and covering the modules to prevent light from entering the liquid reservoir to deter algal/microbial growth in the PLS system. Life support systems are what make human travel a possibility. In long range space travels, such as the travel to Mars, life support cannot depend upon storage alone, it requires a fully regenerative system as well, i.e. waste must be reclaimed for reuse. Steam reformation, supercritical water oxidation, electrochemical oxidation, and incineration are a few of the solid waste reclamation technologies that are being developed and tested for use in space travel. Currently though, it seems that incineration might be the best choice among the previously mentioned, in providing a fully regenerative system. Through rapid conversion, incineration of the inedible parts of wastes and crops produces carbon dioxide, water, and minerals. Incineration is already the most thoroughly developed technology for use in a terrestrial environment. However, with the use of incineration in a closed environment, there is the eventual buildup of pollutants that are emitted in the process. Important things to consider when developing a flue gas clean up technology for use in long range space travels are safety, energy requirements, sustainability, and doable under a micro-gravity condition.

Due to the sensitivity and restrictions of space missions, a flue gas clean up system lacking in any of these considerations can be hazardous and could potentially compromise the missions. Technologies requiring things such as expendables or the use of catalysts are unsuitable for space missions due to the loss of valuable resources and the possibility of catalyst poisoning thus limiting the life-span of a catalyst. Also, due to the micro-gravity, it is difficult to use wet processes that handle liquids, such as spray absorbers. Consequently, even though there are numerous flue gas clean up technologies developed , taking into consideration the limitation each provides, the number of reliable and applicable systems seem to be dwindling. Commercial activated carbon, made mostly from materials such as coconut shells and coal, has been studied for the adsorption and/or reduction of NOx and SO2 . In this paper, we study the use of the activated carbon prepared from hydroponic grown wheat straw and sweet potato stem for the control of air pollutants that are a result of incineration during space travel. Both wheat straw and sweet potato stalk are inedible biomass that can be continuously produced in the space vehicle. It was found that there is actually a minuscule amount of SO2 in the flue gas from the incineration of hydroponic biomass, and that most of the sulfur from the biomass ends up as sulfate in flyash. Since SO2 should have already reacted with the alkali metal, the technique entails the carbonization of the wheat straw and sweet potato stalk, resulting in an activated carbon for the adsorption of NOx and then a reduction of the adsorbed NOx by carbon to form N2. Since most NOx in flue gas from combustion is in the form of NO, and NO2 is readily adsorbed on the activated carbon, this paper concentrates on the removal of NO.