The Enclosure

The shape of an ecosystem relative to its controlling physical and energy parameters can be crucial. In the case of aquatic systems, the relative thickness of the water mass and its relationship to the bottom establish the basic character of an ecosystem. A large body of water would be dominated by true plankters, normally living most of their lives suspended in mid and surface waters, with little benthic (or bottom) influence, whereas the shallow stream or narrow lagoon of a few meters in depth is benthic dominated. Light enters only through the air-water interface of a water ecosystem, and the shape of the containing body of water relative to depth, as well as water turbidity, determines the photosynthetic versus heterotrophic character of the ecosystem. The direction of current flow and wave action through an aquatic system relative to the position and orientation of its communities is critical to simulate in any model. The direction, frequency, and strength of wind relative to forest or field size can also be critical to systems function, as can be the physical dimension and density of such ecosystems.

The all-glass or acrylic aquarium box, ranging from about 401 (10 gallons) to 10001 (250 gallons), is a standard piece of equipment in terrestrial and aquatic modeling, and by drilling holes to attach pipes and linking all-glass tanks in complex arrays, many aspects of wild ecosystems can be modeled with reasonable accuracy.

The construction of molded fiberglass tanks or poured concrete or concrete block tanks, sealed with a wide variety of newer sealants, has considerable advantages for larger systems.

Ideally, the ecosystem envelope would be like that of the boundary of the mathematical modeler, a theoretical boundary allowing the controlling of exchange but not having any inherent characteristics. Walls, whatever their nature, unless rather esoteric measures are used to prevent organisms and organic molecules from using their surfaces, or blocking wind or current, are intrusions into the model ecosystem that may or may not be acceptable. For a small model of a planktonic system, the presence of uncleaned walls may prevent the system from being plankton dominated. To some degree, walls also interact with the water and atmosphere of the ecosystem they contain. For most purposes, glass and many plastics are ideal in this respect.

Greenhouse walls and roofs can block ultraviolet light and, for most ecosystem models, a component of artificial light is probably essential to achieve both the intensity and spectral veracity of natural light. Reinforced cement block or concrete can be valuable construction materials for large systems; however, concrete interacts with both water and atmosphere, being one of the limiters of veracity in of Biosphere II (as we describe below), and must be sealed with epoxy or other, carefully considered resins (Figure 1).

Many chemical elements and compounds used in construction are toxic. Some of these are only mildly poisonous and are often required by organisms as elements in small quantities and only become toxic in excess. Others are always toxic and only concentration determines effect. Glass, acrylics, epoxies, polyesters, polypropylenes, polyethylenes, nylons, Teflon, and sili-cones, among others, are structural materials commonly

Figure 1 Florida Everglades mesocosm during construction. The butyl rubber-lined concrete block walls were used to constrain the entire system as well as to physically separate the salinity subcomponents thereby creating a salinity gradient. The plastic box at the lower right contains the tide controller, which determines the tide level in the estuary (center tank and the four smaller units behind).

Figure 1 Florida Everglades mesocosm during construction. The butyl rubber-lined concrete block walls were used to constrain the entire system as well as to physically separate the salinity subcomponents thereby creating a salinity gradient. The plastic box at the lower right contains the tide controller, which determines the tide level in the estuary (center tank and the four smaller units behind).

used in model/greenhouse construction. When properly cured these materials are generally inert, nonbiodegrad-able, and nontoxic. Many metals and organic additives easily find their way into construction processes and must be avoided or sealed off.

Worm Farming

Worm Farming

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