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Biosphere 2 Mesocosms

The following material has been copied from the Biosphere 2 website research pages.

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Table 1:  Biosphere 2 facts.

Mesocosm Air volumes (m3) Areas (m2)
Agroforestry 35222 2000
Rainforest 26700 2000
Savanna/ocean 41500 2500
Desert 18000 1400

Biosphere 2 and a group of external scientists have been conducting a facility assessment to quantify current capabilities. Suggested changes necessary to implement fully controlled scientific experiments have been made in the rainforest and agro-forestry regions. Recent modifications include the installation of a CO2 control system to adjust internal CO2 levels to programmed set points, air circulation fans to help reduce thermal stratification, continuous trace gas monitoring system, and movable partitions to isolate the rainforest and divide the agro-forestry into three separate sections.

Airflow, trace gas sampling, CO2 injection and partition placement with Biosphere 2 Centre.

The continuous trace gas monitoring system (see Figure) consists of an air sampling system and a gas analysis system. Air pumps draw air at approximately five liters per minute from the rainforest, savanna, desert, and agricultural areas in Biosphere 2 and from one external location. Currently, the system is set up for analyses of methane (CH4) and nitrous oxide (N2O) on a continuous basis and manual canister filling for other gas analyses (N2/O2 ratio, stable isotope analyses, etc.). The system could also supply air samples for the analyses of other gases of interest; for example, isoprene, carbon monoxide, hydrogen sulfide, and terpenes.

Lightweight curtains allow reversible closure of the rainforest and three agro-forestry sections (Figure). The curtains provide isolated `system level' responses (e.g. net ecosystem carbon exchange, transpiration, trace gas production and isotope balances) to changing CO2 and/or other climate factors, allowing comparisons between vegetation types under set experimental conditions. The isolated mesocosm acts essentially like a large static chamber in which fluxes of water, carbon and other compounds can be monitored precisely. The associated data are invaluable to validate models that scale up from leaf to canopy to ecosystem.

These and future modifications will produce unique research opportunities to study `system-level' responses to elevated CO2 and climate changes.

Biosphere 2 water cycle in terrestrial wilderness areas.

Coral Reef Mesocosm

The Biosphere 2 ocean system is ideal for testing models of chemical or biological changes on coral reefs. It is unlike any other artificial reef system, due to its large scale and biological complexity. The unique closure allows whole system manipulations and monitoring that would be extremely difficult in a natural environment. Physical and chemical parameters such as mixing, gas exchange, nutrient concentrations, and partial pressure of CO2 can be independently manipulated.

The Biosphere 2 ocean simulates a Caribbean reef. It is a large tank with a surface area of 35 x 20 meters (100 x 60 feet). Consisting of a southern portion seven meters deep (21 feet) and a northern shallow lagoon, partially separated by a fringing reef (Figure 4). The mesocosm is housed within a high grade, corrosion resistant 6XN stainless steel container. During construction this steel was coated with a paint epoxy resin to hinder corrosion and to reduce leaching of metals into the ocean water. The total water volume of the Biosphere 2 ocean is roughly 2,600,000 liters (676,000 gallons). The system houses about 35 species of hard corals, 25 species of fish, 30 species of algae, and over a hundred invertebrate species.

Figure 4:  Surface plot of Biosphere 2 ocean floor.

The reef system is totally enclosed as other mesocosm within Biosphere 2.  Unlike most aquaria, animals are not fed. In fact, this ocean is big enough to allow its organisms to rely on the internal food chain supported by algae and coral photosynthesis. Light levels are relatively low due to a combination of latitude (32.5 North outside of the tropical reef belt) and shading by the overhead glass and space frame structure. Nonetheless, the measured rates of primary productivity, calcification and nutrient uptake are comparable to those of tropical reefs. Survival of hundreds of species with minimal husbandry over almost a decade demonstrates that the system and its food web are largely self-sustaining.

Four principal types of substrate were incorporated into the reef: Arizona calcium carbonate-rich clay, Arizona limestone boulders and rocks, Caribbean limestone rubble, and Caribbean aragonite sand. Crushed oyster shells fill the cracks and crevices between large rocks. Aragonitic sand covers the foundation sediments in the deep ocean, the lagoon, and the beach.

Numerous mechanical systems simulate or substitute for natural environmental processes. A wave generator and a series of five air-lift pumps, are currently available to circulate water within the tank. Only the wave generator is in continuous use. A series of centrifugal pumps circulate water from the ocean to a separate room where the water is supplied to large experimental flow-through tanks and to heat exchange units. Two heat exchange units control the temperature of the ocean. They consist of large tubs containing plastic coils fed with hot or cold water from the Biosphere 2 Energy Center. Manually operated ball valves control the flow of hot and cold water through the coils. A series of filtration systems were initially installed, including algal turf scrubbers, protein skimmers, plate filters, and rotary drum filters. Over the last two years, it has been recognized that the ocean biota is very efficient at recycling nutrients and all mechanical filtration has been interrupted. Nutrient concentrations, monitored weekly, are very low, characteristic of tropical coral reefs.

Our current research directives require that the condition of the ocean be closely monitored with electronic sensors and weekly sampling routines (Figure 5).

Ocean sensor data for 01-Jul-97 thru 07-Dec-98. The data are hourly averages from a single
point within the mesocosm.

Terrestrial Research

Concentration of atmospheric CO2 is now 30% higher (about 360 ppmv) than at the beginning of the industrial revolution (280 ppmv in 1800). With increasing fossil fuel combustion and changing land usage, elevated concentrations of CO2 and other greenhouse gases (e.g., methane, nitrous oxide) are predicted to increase global air temperature.

The combined impact of changing climate and trace gas concentration on terrestrial ecosystems is poorly understood. Experimental and modeling approaches represent two means to achieve an understanding, hence integrating both approaches will accelerate global change research.

Although ecophysiological processes measured at the leaf level, such as photosynthesis and energy balance, are relatively well understood, small-scale measurements may have little relevance for predicting large-scale processes. Figure 6 shows how simulation models, coupled with Geographic Information Systems (GIS) and remote sensing can be used for scaling from leaf level measurements to entire ecosystmens. Clearly, a major challenge will be to integrate how microenvironments as well as whole biotic entities respond in these niches. Biosphere 2 offers the potential to link measurements and modeling from leaf to single plant to whole ecosystem levels in one controlled experimental facility.

Integrated approach to scaling ecophysiological processes from the leaf to the ecosystem level.

Terrestrial ecosystem research at Biosphere 2 examines possible impacts of elevated CO2, water deficit, high temperature, and nutrient loading on ecosystem structure and function. Our research also seeks to determine the roles that these ecosystems play in regulating global climate. Current experiments in the wilderness mesocosms are linked to the development, calibration, and validation of ecophysiological models that predict dynamics of natural and managed ecosystems. While the wilderness area offers the potential to investigate specific processes in complex mesocosms, the agro-forestry area allows investigations of responses of a few cultivated species at a time, with an initial focus on managed forests under global change conditions.

No other facility exists with as large a controlled environment space (1,500 m2 planting area, 15 m high on average; soil and atmospheric volumes of approximately 2,000 m3 and 38,000 m3, respectively), allowing experiments investigating CO2, management (primarily water and nitrogen) and temperature interactions.

Trace gases such as carbon dioxide, methane, nitrous oxide, methyl chloride, methyl bromide, carbonyl sulfide, carbon tetrachloride, chloroform, and isoprene all play important roles in the chemistry of the earth's atmosphere, and thus in modulating climate and the ozone layer. The main goal of the trace gas group at Biosphere 2 is to understand how terrestrial ecosystems influence the concentration of trace gasses in the atmosphere and how they depend on environmental variables. Current research interests are isoprene, methane, methyl chloride, methyl bromide, and nitrous oxide. Several features give Biosphere 2 a critical advantage for this type of research: 1) lack ultraviolet light in Biosphere 2 2) large biomass to atmosphere ratio, which amplifies biotic effects on atmospheric chemistry 3) no anthropogenic sources, and 4) chemical and physical manipulations of the system are possible.

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