Closed Ecosystem Research Articles

Automated system for cleaning liquid waste products for closed ecosystems for space purposes

Ensuring human life activity for several years in isolated conditions of future Martian and lunar bases is possible with the organization of a circular process of converting organic waste, including human exometabolites (cal, urin), into the products he needs: water, oxygen and food. A promising way to organize such a circular process is to create a three–link closed ecosystem (CES): a person, a link for obtaining fertilizers from organic waste and plants - where plants synthesize the products necessary for a person. The paper considers the original scheme of a complex installation for the purification of liquid products of processing of human exometabolites from pollutants in the process of obtaining nutrient solutions for growing plants in a CES. The processing of human exometabolites was carried out in a device for physicochemical oxidation of hydrogen peroxide in an aqueous medium under the action of alternating electric current – in a “wet” combustion reactor. Peripheral equipment was selected for the organization of the automatic control system of the cleaning plant, problems were identified and approaches were developed in the automation of technological processes and the creation of software for human interaction with the proposed installation. Experiments on the cultivation of lettuce plants have been carried out, confirming the effectiveness of the proposed processes of purification of liquid products of processing of human exometabolites. It is concluded that the created integrated cleaning plant, equipped with the proposed software, can be used for scientific research in relation to the subject of CES, including space purposes.

CLOSED ECOLOGICAL SYSTEMS: FROM THE BIOSPHERE TO LIFE SUPPORT SYSTEMS AND BACK

The paper provides a brief overview of the available facts and ideas about the nature of climate change. Theproblems of ecological research, which are becoming more acute in relation to biosphere research, are considered: this is the problem of data deficit and the problem of the uniqueness of ecosystems. The key difference between the biosphere and natural ecosystems is highlighted, which ensures the long-term, in the ultimate perspective infinite, existence of the biosphere – the existence of a balance of biogen cycles or the closure of the flows of substances. The advantages of laboratory closed ecological systems (CES) as tools for experimental and theoretical study of the biosphere are considered. The contribution of the most well-known CES (BIOS-3, Folsom microcosms, Biosphere-2, micro-CES) to the understanding of biospheric processes is discussed. The problems and paradoxes identified in the mathematical modeling of CESs (Vernadsky-Darwin paradox, limitations of models of rigid metabolism), which are closely related to the well-known ecological paradoxes of May and Hutchinson, are discussed. A flexible metabolism approach is proposed to reduce the severity of these paradoxes. The measures proposed within the framework of so-called “green initiative” are discussed from the position of “biosphere as a CES”. Among these measures are reducing the carbon footprint of pets, migration to electric vehicles and renewable energy sourcesб and carbon sequestration by trees. The seriousness of biosphere-climatic changes problem is emphasized, which cannot be resolved without accounting the closure of substance flows in the biosphere.

The Evolutionary Mechanism of Formation of Biosphere Closure

In accordance with the ideas of V.I. Vernadsky, the Earth’s biosphere can exist only because of the high degree of closure of the cyclic matter transformations carried out by all living organisms by using the energy from the Sun. In the course of its evolution, the Earth’s biosphere has undergone a number of cardinal transformations, but, at least for the last 20 million years, the gas composition of the atmosphere, and primarily the concentration of carbon dioxide, has remained practically unchanged. Nevertheless, the high degree of closure of material flows in the Earth’s biosphere seems paradoxical, since closure is not an adaptive feature of an individual undergoing natural selection for traits that give an advantage here and now (the Vernadsky–Darwin paradox). The stages in the formation of the closure of the Earth’s biosphere are considered in the context of four epochs that differ in the energy available to living organisms: (1) geochemical energy; (2) solar energy; (3) energy of oxidative phosphorylation; and (4) consumption of living flesh, predation. The paper considers possible options for resolving the VD paradox using as the example models of closed ecological systems (CES) with low species diversity. The fundamental inapplicability of ecological models with rigid metabolism for the description of CES is shown. Three mechanisms for resolving the VD paradox are proposed and the conditions for their implementation are assessed: (1) a stochastic mechanism: random selection of closing organisms (decomposers) with the corresponding stoichiometric ratios; (2) changing the consumption stoichiometry by switching catabolic pathways to different types of substances (proteins, fats, carbohydrates); and (3) changing the consumption stoichiometry by choosing food, depending on the state of internal nutrient pools. The present study leads to the conclusion that the Vernadsky–Darwin paradox can be resolved in nature by combining the mechanisms that simultaneously provide both a current competitive advantage and the ability to close trophic chains with a wide variation in the composition of material flows.

Photobiological Efficiency of Radiation of LED Radiators for Cenoses of Different Age Plants in Relation to Conditions of Closed Ecosystems

The paper presents experimental data on the photo-biological efficiency of the emission of white light LED irradiators and phyto-spectrum with an intensity of 460 μmol/(m2s) and 800 μmol/(m2s) at the intermediate (18 days) and final (27 days) stages of the growing season of growing Chinese cabbage (Brassica rapa), chard (Beta vulgaris), and radish (Raphanus sativus) in relation to the conditions of closed ecosystems (CES). The presence of different specifics of the reaction of plants to the spectral composition of radiation, both at the intermediate and final stages of vegetation, has been established. It has been suggested that in some plant species (Chinese cabbage) it may be physiologically justified at the intermediate stage of vegetation to change the spectral regime of irradiation from the phytospectrum to white light in order to achieve higher productivity values. Using the example of chard, it has been established that the phyto-spectrum can be more effective than white light when growing leaf biomass, regardless of the growing season. Using the example of radishes, it was shown that the phytospectrum stimulates the accumulation of high values of above-ground biomass in comparison with white light, however, for the accumulation of root biomass in relation to the conditions of the CES, it is more expedient to use white light, since with a biomass of root crops comparable to the phytospectrum, plants with an increased coefficient of economic efficiency are formed in white light, which reduces the share of waste in the CES (inedible leafy biomass). On the basis of the data obtained, possible tasks of scientific research on evaluating the spectral efficiency of radiation at certain stages of plant vegetation, as well as the prospects for creating LED irradiators with a physiologically based program for regulating the spectral composition and radiation intensity, are discussed.

Possible risks for the functioning of cyclic processes in the experimental model of a closed ecosystem

The purpose of the present study is to consider a number of possible risks that may emerge when processed human wastes are involved into mass exchange processes as fertilizers for plants cultivated in the experimental model of the closed ecosystem (CEEM). The problems relating to the disruption of cycling processes in closed ecosystems can be tentatively divided into two groups: the problems that can be rather easily overcome and the chronic problems. Addition of plant inedible biomass to the soil-like substrate (SLS) can result in a decrease in plant productivity because of allelopathic interactions and enhanced growth of microorganisms. The 30% decrease in wheat productivity by the end of long-duration experiments in the CEEM, with plants grown on quasi-non-renewed solutions based on liquid products prepared by physicochemical mineralization of human wastes, was caused by lower resistance of the plants affected by toxicants accumulated in the solution because of incomplete mineralization of the wastes. The reason for the differences between the macronutrient inflows and outflows was that the donor of human wastes followed a European-type diet while the system produced only part of the plant-based diet. Moreover, macronutrients were partly sorbed in rooting substrates and became unavailable to plants: the substrates in the system retained about 50% of the Ca and 20% ÷ 25% of the Mg, Na, and P inflows over one cycle. These problems are temporary and can be minimized in the foreseeable future.

Hierarchical Control of Space Closed Ecosystems: Expanding Microgrid Concepts to Bioastronautics

One of the main challenges of human space exploration is the development of artificial ecosystems, which can be used as life support systems (LSSs) to enable long-duration human space missions. In an open LSS, no food generation or waste treatment is provided in space, and supplies from Earth are necessary. According to Figure 1, considering the approximate metabolic consumables and hygiene water as well as the number of crewmembers [1], a huge mass would be required to be transported from Earth, which brings the necessity of a regenerative or closed LSS [2]-[4]. Closed ecological systems (CESs) are ecosystems without any matter exchange with the outside environment [2]. The most advanced humanmade CESs include Advanced Life Support System Test Bed (ALSSTB) (the NASA Johnson Space Research Center, Houston, Texas), Biosphere 2 (Oracle, Arizona), BIOS-3 (Krasnoyarsk, Russia-no longer operative), the Closed Ecology Experiment Facility (CEEF) complex (Rokkasho, Japan), the Micro-Ecological Life Support System Alternative (MELiSSA) Pilot Plant (MPP) (Universitat Aut?noma de Barcelona, Spain), and the Concordia Antarctica Station, which are different from one another with respect to their complexity, size, and degree of closure [2]. CESs are necessary for long-term manned space missions, which aim to minimize support from Earth. They are composed of several specific compartments that, together, reproduce the main functionalities of an ecological system in a continuous mode of operation and under controlled conditions.

Modeling of biotic cycle formation in closed ecological systems

The biotic turnover formation in closed ecological system (CES) is analyzed by means of mathematical and computer modeling. The model CES hierarchical structure formation is ruled by the energy flow through the ecosystem which increases after the introduction of a predator in the steady state of “production - reduction” systems. The model analysis shows that the presence of the primary predator under certain conditions leads to the acceleration of the biotic turnover because of its higher mineralization ability (in comparison with the same of decomposer). The most acceptable predator which is able to bring the system towards the higher biotic turnover rate and energy consumption can be found for each system.

Why did carbon become the pseudo-limiting factor in aquatic closed ecological systems?

Closure from the earth's atmosphere is a critical test of an ecosystem's ability to function. In our earlier testing of autotrophic Closed Ecological Systems (CESs), a C:N ratio of 26.4 (3.3 mM NaHCO3 and 0.125 mM NaNO3) supported algal and Daphnia populations for months, but developed extreme pH values (∼11 ungrazed, >10, grazed), suggesting that the systems were carbon-limited. Only approximately half the HCO3- (bicarbonate) would be expected to be available to green algae, the other portion becoming CO3−2 (carbonate). In an experiment described here, CESs were developed to explore a greater range of C:N ratios. To keep the medium from becoming too osmotically concentrated, NaNO3 was reduced to 0.0312 mM and NaHCO3 tested at 3.3, 13.2, and 26.4 mM, resulting in nominal C:N ratios of 105, 422, and 845. However, additional carbon was not beneficial to long-term survival of the organisms. The algal abundance was relatively insensitive to C:N ratio; greater concentrations of C were not beneficial. Daphnia populations were sensitive to C:N ratio and persisted longer at the lowest C:N ratio of 105. All of the C:N ratios tested in these CESs are outside of the expected range suggested from ecological studies, which is based on the Redfield Ratio of 6.625 C:N, the expected chemical composition of algae. Two potential explanations for the apparent high C demand in our CESs are suggested by the literature. The first is production of fatty algal cells, e.g., one of the algal species, Scenedesmus obliquus, is reported to produce high-lipid cells that could have a higher C:N ratio than the Redfield Ratio. The second is “carbon overconsumption,” which has been suggested for N-limited marine phytoplankton communities dominated by diatoms or nutrient deficient algal communities dominated by small cells that are under-represented by chlorophyll a measurements. The unexpected C dynamics found in our CES tests could be relevant to the design of biological life support systems that must be provisioned with adequate elements for long-term ecosystem functionality. If the actual demand for C is underestimated, its storage may be inadequate.

Analysis of the gas exchange and water balance in a closed experimental model of the artificial ecosystem intended for an estimated portion of a human

This study was performed to investigate water and gas exchange in the experimental model of a closed ecological system (CES) intended for an estimated portion of a human in the long-duration (several-month) experiment. The diversity of the vegetable conveyor in the system was increased. Human wastes were involved in mass exchange processes, and human respiratory function was periodically connected to the experimental model of a CES. The experimental model of a CES was used to quantify regeneration of the gaseous atmosphere with oxygen and carbon dioxide loops by linking the photosynthesizing compartment with the heterotrophic compartment (soil-like substrate) and by the periodic connection of the human respiratory function. Under the preset light and temperature conditions, atmospheric CO2 concentration in the CES model intended for a portion of a human was maintained at a level that neither limited photosynthetic processes nor was harmful to humans (800–2000 ppm) during the 154-day experiment. At the same time, O2 concentration did not either drop below 20.8% or rise above 22.6%. The amount of the evapotranspiration water collected in the system could satisfy 50% of the daily water requirement of a human (with all the water used and excreted by the human being processed and used to irrigate plants). The evapotranspiration water did not need to be additionally purified before being used by humans. Thus, in the experimental model of the closed ecological system, human oxygen and food requirements (per 0.05 portion of a human) were matched to the function of the heterotrophic compartment and the photosynthesizing activity of the multispecies uneven-aged higher plant community.

Pressure, O2, and CO2, in aquatic Closed Ecological Systems

Pressure increased during net photosynthetic O2 production in the light and decreased during respiratory O2 uptake during the dark in aquatic Closed Ecological Systems (CESs) with small head gas volumes. Because most CO2 will be in the liquid phase as bicarbonate and carbonate anions, and CO2 is more soluble than O2, volumes of gaseous CO2 and gaseous O2 will not change in a compensatory manner, leading to the development of pressure. Pressure increases were greatest with nutrient rich medium with NaHCO3 as the carbon source. With more dilute media, pressure was greatest with NaHCO3, and less with cellulose or no-added carbon. Without adequate turbulence, pressure measurements lagged dissolved O2 concentrations by several hours and dark respiration would have been especially underestimated in our systems (250–1000ml). With adequate turbulence (rotary shaker), pressure measurements and dissolved O2 concentrations generally agreed during lights on/off cycles, but O2 measurements provided more detail. At 20°C, 29.9 times as much O2 will distribute into the gas phase as in the liquid, per unit volume, as a result of the limited solubility of O2 in water and according to Henry’s Law. Thus even a small head gas volume can contain more O2 than a larger volume of water. When both dissolved and gaseous O2 and CO2 are summed, the changes in Total O2 and CO2 are in relatively close agreement when NaHCO3 is the carbon source. These findings disprove an assumption made in some of Taub’s earlier research that aquatic CESs would remain at approximately atmospheric pressure because approximately equal molar quantities of O2 and CO2 would exchange during photosynthesis and respiration; this assumption neglected the distribution of O2 between water and gas phases. High pressures can occur when NaHCO3 is the carbon source in nutrient rich media and if head-gas volumes are small relative to the liquid volume; e.g., one “worse case” condition developed 800mmHg above atmospheric pressure and broke the glass container. Plastic screw cap closures are likely to leak at high pressures and should not be assumed to seal unless tested at appropriate pressures. Pressure can be reduced by having larger head-gas volumes and using less concentrated nutrient solutions. It is important that pressure changes be considered for both safety and closure, and if total O2 is used as the measure of net photosynthesis and respiration, the O2 in the gas phase must be added to the dissolved O2.

Contingency and Statistical Laws in Replicate Microbial Closed Ecosystems

Contingency, the persistent influence of past random events, pervades biology. To what extent, then, is each course of ecological or evolutionary dynamics unique, and to what extent are these dynamics subject to a common statistical structure? Addressing this question requires replicate measurements to search for emergent statistical laws. We establish a readily replicated microbial closed ecosystem (CES), sustaining its three species for years. We precisely measure the local population density of each species in many CES replicates, started from the same initial conditions and kept under constant light and temperature. The covariation among replicates of the three species densities acquires a stable structure, which could be decomposed into discrete eigenvectors, or "ecomodes." The largest ecomode dominates population density fluctuations around the replicate-average dynamics. These fluctuations follow simple power laws consistent with a geometric random walk. Thus, variability in ecological dynamics can be studied with CES replicates and described by simple statistical laws.

Non‐intrusive monitoring of atmospheric CO2 in analogue models of terrestrial carbon cycle

Summary1. Closed ecological systems (CES) are small man‐made ecosystems which do not have any material exchange with the surrounding environment. Recent ecological and technological advances enable successful establishment and maintenance of CES, making them a suitable tool for detecting and measuring subtle feedbacks and mechanisms.2. As a part of an analogue (physical) C cycle modelling experiment, we developed a non‐intrusive methodology to control the internal environment and to monitor atmospheric CO2 concentration inside 16 replicated CES. Whilst maintaining an air‐tight seal of all CES, this approach allowed for access to the CO2 measuring equipment for periodic re‐calibration and repairs.3. To ensure reliable cross‐comparison of CO2 observations between individual CES units and to minimize the cost of the system, only one CO2 sampling unit was used. An ADC BioScientific OP‐2 (open‐path) analyser mounted on a swinging arm was passing over a set of 16 measuring cells. Each cell was connected to an individual CES with air continuously circulating between them.4. Using this setup, we were able to continuously measure several environmental variables and CO2 concentration within each closed system, allowing us to study minute effects of changing temperature on C fluxes within each CES. The CES and the measuring cells showed minimal air leakage during an experimental run lasting, on average, 3 months. The CO2 analyser assembly performed reliably for over 2 years, however an early iteration of the present design proved to be sensitive to positioning errors.5. We indicate how the methodology can be further improved and suggest possible avenues where future CES based research could be applied.

Community metabolism of aquatic Closed Ecological Systems: Effects of nitrogen sources

To investigate the effect of nitrogen sources on Closed Ecological Systems (CESs), three nitrogen sources (NaNO 3, sodium nitrate; NH 4Cl, ammonium chloride; and NH 4NO 3, ammonium nitrate) were each tested in freshwater CESs consisting of a chemically defined medium, three species of green algae ( Ankistrodesmus, S cenedesmus, and Selenastrum), the grazer Daphnia magna, and associated microbes, under 12 h light/12 h dark cycles. It had been hypothesized that the development of high pH in earlier CESs was the result of nitrate utilization, and that ammonium might result in acid conditions, while ammonium nitrate might result in more moderate pH. The three nitrogen sources supported similar densities of algae (estimated by in vivo fluorescence) and similar Daphnia populations. The experiments showed that pH levels rapidly increased when grazers were absent or at low abundances irrespective of the nitrogen source. Consequently, it is hypothesized that carbon cycles, rather than nitrogen sources, are responsible for the pH dynamics. Oxygen diurnal (light:dark) cycles tended to come into balance more quickly than pH. It may be more feasible to convert O 2 data to energy units (using “oxycalorific” values) than CO 2 data since CO 2 dynamics may include other chemical reactions than just photosynthesis and respiration. The feasibility of sustaining grazer populations for at least several weeks in small, simple CESs was demonstrated, along with the ability to monitor algae-grazer dynamics, and the recording of O 2 and pH measurements.

Contributions of cellulose to a microbial-algal-Daphnia food chain in Closed Ecological Systems

(2009). Contributions of cellulose to a microbial-algal-Daphnia food chain in Closed Ecological Systems. SIL Proceedings, 1922-2010: Vol. 30, No. 8, pp. 1259-1263.

Tightly closed ecological systems reveal atmospheric subtleties – experience from Biosphere 2

Processes which produce slow changes in air composition in a closed ecological system (CES) may not be noticed if the leak rate of the CES is significant. Dilution of the system’s air with outside air can mask these processes. A tightly closed CES provides the opportunity for slow changes to accumulate over time and be observed and measured. Biosphere 2 (volume 200,000 m 3) had a low leak rate of less than 10 percent per year. Oxygen declined slowly at varying rates reflecting seasonal influences, which averaged to about 140 ppm per day during the first 16 months of the two-year closure. Computer simulations of the observed rate of oxygen loss combined with other hypothetical leak rates suggest that the decline would have been hidden by a leak rate as low as one percent per day. Sealing Biosphere 2 involved rigorous design specifications and inclusion of two expansion chambers (called “lungs”) to accommodate expansion/contraction of the atmosphere, which enabled limiting the pressure difference between inside and outside atmospheres to the range of ±8 Pa (0.08 mBar). Measurement of leak rate was by two methods: the first, measuring the rate of deflation of the lungs while holding a constant elevated pressure differential enabled calculation of an estimated leak rate within the usual operating pressure differential range; the second was to measure the progressive dilution of trace gases spiked into the atmosphere. Both methods confirmed leakage to be less than 10 percent per year. Operational data from the 40 m 3 Laboratory Biosphere is used to illustrate how normal variations of temperature, humidity and barometric pressure would combine to force leakage and rapidly dilute the internal atmosphere if it were not equipped with a lung. It is demonstrated that very high degrees of closure for a CES enable experimental observation of small imbalances in atmospheric cycles or slow accumulation of trace gases that could otherwise be masked by dilution with atmosphere external to the CES.

Naturally deducing estimate for the coefficient of celss closure

The term Closed Ecological System (CES) is in wide use. However there is no generally accepted measure of the closure of ecological systems. In order to obtain reproducibility of experiments with natural and man-made CES (with respect to degree of closure) some universal estimate needs to be developed. Understanding ecological systems as a network and closure as the degree of matter recycling allows the use of matrix graphs. Graphs are very natural forms for the presentation of the network of matter flows in ecosystems. An estimate equal to the sum of products of weights of oriented edges that constitute contour is suggested as a measure of the degree of closure in ecosystems. It is shown that this estimate can be uniformly applied to ecosystems of arbitrary size and configuration of flows.

Formation of higher plant component microbial community in closed ecological system

Closed ecological systems (CES) place at the disposal of a researcher unique possibilities to study the role of microbial communities in individual components and of the entire system. The microbial community of the higher plant component has been found to form depending on specific conditions of the closed ecosystem: length of time the solution is reused, introduction of intrasystem waste water into the nutrient medium, effect of other component of the system, and system closure in terms of gas exchange. The higher plant component formed its own microbial complex different from that formed prior to closure. The microbial complex of vegetable polyculture is more diverse and stable than the monoculture of wheat. The composition of the components’ microflora changed, species diversity decreased, individual species of bacteria and fungi whose numbers were not so great before the closure prevailed. Special attention should be paid to phytopathogenic and conditionally pathogenic species of microorganisms potentially hazardous to man or plants and the least controlled in CES. This situation can endanger creation of CES and make conjectural existence of preplanned components, man, specifically, and consequently, of CES as it is.

Computer modeling of the biotic cycle formation in a closed ecological system.

The process of biotic turnover in a closed ecological system (CES) with an external energy flow was analyzed by mathematical modeling of the biotic cycle formation. The formation of hierarchical structure in model CESs is governed by energy criteria. Energy flow through the ecosystem increases when a predator is introduced into a "producer-reducer" system at steady state. Analysis of the model shows that under certain conditions the presence of the primary predator with its high mineralization ability accelerates the biotic turnover measured by primary production. We, therefore, conclude that for every system it is possible to find a suitable predator able to provide the system with a higher biotic turnover rate and energy consumption. Grant numbers: 99-04-96017/2000.

Impaired growth of plants cultivated in a closed system: Possible reasons

Plants in experiments on “man-higher plants” closed ecosystem (CES) have been demonstrated to have inhibited growth and reduced productivity due to three basic factors: prolonged usage of a permanent nutrient solution introduction into the nutrient medium of intra-system gray water, and closure of the system. Gray water was detrimental to plants the longer the nutrient solution was used. However, higher plant growth was mostly affected by the gaseous composition of the CES atmosphere, through accumulation of volatile substances.

Indications and counterindications for applying different versions of closed ecosystems for space and terrestrial problems of life support

Different versions of manned closed ecosystems (CES) based on photosynthesis of unicellular and/or higher plants and chemosynthesis of bacteria are considered. Different versions of CES have been compared for applying them on Earth, Moon, Mars and Venus orbital stations, for Mars missions and planetary stations as well as to provide high-quality life in extreme conditions on the Earth. In mycrogravity we recommend CES with unicellular organisms based on photosynthesis or chemosynthesis (depending of the availability of the light or electric energy). For the planetary stations with Moon gravity and higher CES with higher plants are recommended. Improvement of indoor air quality by CES biotechnology is considered.