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Species Increase „When Rare? _

Successful Invasion Store Characteristics

FIGURE 5.10 A successional algorithm diagram for developing diversity in a model community. (Adapted from Drake, J. A. 1990a,b. TREE 5:159-164.)

Error Eliminator and Innovator

Reward Loop Reinforcement of Loop Flow

Error Eliminator and Innovator

Reward Loop Reinforcement of Loop Flow

FIGURE 5.11 Two different views of the loop reinforcement model. This model represents the self-organization process in succession. (From Odum, H. T. 1971. Environment, Power, and Society. John Wiley & Sons, New York. With permission.)

which must be visited only once (Haggett and Chorley, 1969; Lowe and Moryadas, 1975). The different stages that succession passes through might be analogous to the towns that the salesman must visit. In this context the succession diagram with multiple pathways in the old ecological literature might provide a library of possible solutions to minimum-distance problems. However, these diagrams only show the successful links, and it may be necessary to have knowledge about links that have been selected against (i.e., towns not visited by the salesman or possible successional stages that don't occur). The travelling salesman problem is addressed with ant colony behavior by Dorigo and Gambardella (1997).

What is being suggested here is not a simulation model, such as shown in Figure 5.8, but rather a more generalized algorithm that could be adapted for abstract problem solving. H. T. Odum's (1971) loop reinforcement model may represent a possible starting point because it includes both a feedback phase and a selection phase, like evolution or learning (Figure 5.11). The quote listed below provides a summary of H. T. Odum's (1971) concept:

Consider the central principle of self-design, which is often misunderstood and opposed as nonmechanical teleology by those who do not understand the network nature of the environment. Systems readily develop towards their successful purpose by a process which essentially may be the same essence as thinking of the brain. Systems have purpose just as people do, for both are highly mechanical and readily understood as causal processes. The self-organizing process by which a system develops a network of insulated mineral and food pathways is a special case of a process that may be termed in circuit nomenclature as "loop reinforcement" ... .

If the various possible pathways which are first attempted by organisms invading or evolving in a place are greater in number and variety than those which can emerge finally on the available energy budget, the ones which will prevail will be those that have a positive feedback loop since these are reinforced by resources which are drained away from those circuits not receiving loop reinforcement. In other words, the processes believed to occur in learning within an organism and the process of organizing an ecosystem are essentially the same ... An ecosystem is learning when it is under successional development.

Information about succession is stored in the collective trophic and life history strategies of species that exist in the seed sources and seed banks of the landscape. This information is transmitted through time as succession proceeds and is a template for future successions. Margalef (1968) outlined similar mechanisms in his discussion of succession.

The goal in the computational effort proposed above is to develop the concept of the ecosystem as a computer. H. T. Odum (1971) briefly outlined this perception when he wrote a short section entitled An Ecosystem as Its Own Computer. His main thrust was to develop simulation models, but a new kind of network epistemology can be seen to emerge from his work (Kangas, 1995). Michael Conrad (1995; Conrad and Pattee, 1970) also has contributed to this work and suggests alternative approaches. The notion of the ecosystem as a computer is the ultimate in the machine analogy (see Chapter 7).

If succession can be harnessed as a form of computation, it might open a whole new area of computational biology. Perhaps the next generation of ecological engineers who learn enough about both engineering and ecology can bridge the present gaps in knowledge and will be able to develop this possibility.

Bioremediation

In some cases restoration may take the form of bioremediation. This approach covers any system that utilizes natural, enhanced, or genetically engineered biological processes to alleviate a pollution problem (Cookson, 1995). In practice, bioremediation usually refers to microbial systems (primarily bacteria and/or fungi) that degrade the pollutant through biological metabolism (i.e., biodegradation). Thus, the pollutant becomes part of the energy signature for these systems. The microbiologist Martin Alexander (1973, 1981) was the first to outline the use of microbes for bioremediation of pollution sources. He put forward the principle of microbial infallibility which states that no natural organic compound is totally resistant to biodegradation, given the appropriate environmental conditions (Alexander, 1965). This is an important idea that is fundamental to all natural ecosystems in relating to biogeochemical cycling. The principle might be restated by saying that nature always recycles. Alexander recognized that some man-made compounds (sometimes termed xenobiotics) resist biodegradation and consequently persist and accumulate in the environment. These are considered to be recalcitrant due to their chemical structure in terms of molecular form and bond sequences. Recalcitrant compounds are of special interest to biochemists because their chemical structure is so exotic that microbes lack enzymes to break them down. Overcoming the barriers to biodegradation of recalcitrant compounds is a primary goal of bioremediation, and Alexander (1994) believes microbial metabolism ultimately can be managed or engineered for this purpose.

The first application of bioremediation that is widely recognized as being successful occurred in 1989 at the Exxon Valdez oil spill in Alaska [Office of Technology Assessment (OTA), 1991]. Oil from the tanker contaminated more than 100 miles (160 km) of beaches along Prince William Sound. Bioremediation was tested by adding fertilizer to the contaminated beaches in order to stimulate natural microbes. Biodegradation was accelerated as much as fourfold over control beaches that did not receive fertilizers. The results of this experiment encouraged much work on bioremediation throughout the 1990s. The two basic methods of bioremediation involve in situ (on site) and ex situ (in bioreactors) applications. In situ methods work for low levels of contaminants and include two kinds of additions to the environment. Biostimulation involves the addition of nutrients which otherwise limit biodegradation by indigenous microbes. Bioaugmentation involves the addition of microbes to the site for cases where the local microflora lacks appropriate species to carry out biodegradation. Ex situ methods work for high levels of contaminants where more control over environmental factors such as temperature and pH is necessary. A final method that can be carried out either in situ or ex situ is the use of microbes that have been genetically engineered for enhanced biodegradation. This approach is highly regulated because of risks associated with introducing these exotic species to the environment (see Chapter 7). One idea that is being studied as a countermeasure is to engineer self-destruct genes into the genetically engineered microbes so that after they break down a pollutant, they will die off and not become invasive. However, use of genetically engineered species is still experimental and not yet a major factor in commercial applications of bioremediation.

Phytoremediation relies on plants for pollutant cleanup (Brown, 1995; Susarla et al., 2002). The primary mechanism is uptake by roots and incorporation into biomass, though other techniques involving oxygenation of the rhizosphere also are used. Some examples of species used in phytoremediation were mentioned in Chapter 2 in relation to sewage treatment: Lemna (duckweed), Typha (cattail), and Eich-hornia (water hyacinth). This approach is best developed for a special class of plants called hyperaccumulators (Brooks, 1998). These plants take up and store much higher concentrations of heavy metals compared with normal plants. Examples include mustard plants (Brassica sp.) and sunflowers (Helianthus sp.). The method is to grow plants in contaminated soil or water and to harvest their biomass as a way to concentrate and remove the pollutants. This is the same approach used in the algal turf scrubber technology described in Chapter 2. The harvested biomass which is now contaminated must be disposed of either by landfilling or by incineration. Genetic engineering is being studied for enhancing phytoremediation potentials but existing applications rely on plants that are naturally preadapted for high uptake rates. Phytoremediation is a relatively new approach for pollutant cleanup and new candidate species are being sought. The spring ephemerals of temperate zone deciduous forests are a group that might lend themselves to phytoremediation. These plants grow quickly and complete their life cycles during the spring time, for the most part before the overhead canopy of trees leafs out. Familiar species of the eastern U.S. include spring beauties (Claytonia sp.), mayapple (Podophyllum peltatum) and jack-in-the-pulpits (Arisaema sp.). These wildflowers are a diverse group with significant nutrient uptake capacity due to their fast growth (Blank et al., 1980). In fact, Muller and Bormann (1976) suggested that spring ephemerals act like a "vernal dam" in absorbing nutrients that might otherwise be lost to the forest nutrient cycle due to leaching by snow melt and spring showers. Could the spring ephemerals be used in some kind of horticultural design for phytoremediation? Another candidate system might be the tropical rain forest subsystem of tree roots and fungal mycorrhizae that carry out direct recycling in the litter layer and upper soil layers. The direct-recycling hypothesis was put forth by Went and Stark (1968a, 1968b) from observations made in an Amazonian rain forest. The idea is that nutrients tend to cycle directly in the tropical trees from decomposing litter back into roots without passing through the mineral soil. The mycorrhizae act as "nutrient traps" by contributing to both decomposition and nutrient uptake (see Figure 5.7). This adaptation is important in tropical rain forests because leaching due to high rainfall can cause rapid removal of nutrients from the rooting zone of the soil. The Went and Stark hypothesis has been supported by experimental work (Herrera et al., 1978; St. John, 1983; Stark and Jordan, 1978) and indications of direct recycling have been found more widely in forests outside of the tropics (Fogel, 1980).

Other, less well-known systems also fall under the heading of bioremediation. For example, John Todd adapted his living machine concept (see Chapter 2) to create a lake restorer system (Todd, 1996a). This is a living machine that floats on a raft on a water body and acts to improve water quality by recirculating water through the system. Water is pumped on to the raft, where it flows through the living machine and then it is discharged back to the water body. Treatment takes place by the same kinds of processes that occur in a treatment wetland (see Table 2.3). An interesting feature of lake restorers is their autonomy. Todd has used a windmill to provide power to run the pump on his systems and a group of University of Maryland students (Yaron et al., 2000) has used solar power (Figure 5.12). The autonomy of these systems means that once created, they theoretically can act independently and with little maintenance. Development of lake restorers is still in early stages but they represent a very interesting state-of-the-art design in ecological engineering, especially because of their potential for autonomous behavior and self-organization. The largest lake restorer built by Todd's group is located in Berlin, MD, on the eastern shore of the state (Shaw, 2001). This system provides final treatment of wastewater from a poultry processing plant. The restorer is located in a lagoon that has been formed into a meandering channel by the installation of curtains of artificial textile

/SOLAR PANEL MOUNTED ON PRESSURE-TREATED WOOD FRAME

1.3cm HOLES

FIGURE 5.12 Views of the University of Maryland lake restorer ecosystem. (Adapted from Yaron, P., M. Walsh, C. Sazama, R. Bozek, C. Burdette, A. Farrand, C. King, J. Vignola, and P. Kangas. 2000. Proceedings of the 27th Annual Conference on Ecosystems Restoration and Creation. P. J. Cannizzaro (ed.). Hillsborough Community College, Plant City, FL.)

1.3cm HOLES

FIGURE 5.12 Views of the University of Maryland lake restorer ecosystem. (Adapted from Yaron, P., M. Walsh, C. Sazama, R. Bozek, C. Burdette, A. Farrand, C. King, J. Vignola, and P. Kangas. 2000. Proceedings of the 27th Annual Conference on Ecosystems Restoration and Creation. P. J. Cannizzaro (ed.). Hillsborough Community College, Plant City, FL.)

that extend from the surface down to the sediments. The restorer system consists of three components: floating piers with racks of aquatic plants that extend out into the channel, the plankton in the channel, and the curtains which are covered with attached macroinvertebrates. Unlike the smaller, autonomous lake restorers, this large system treats the wastewater as it flows through the lagoon. Treatment occurs by spiraling between the three component subsystems as the wastewater moves along the channel (Figure 5.13).

Wastewater

Ocean Eutrophication Ecological System

Water

FIGURE 5.13 Spiraling wastewater treatment in the Ocean Arks' lake restorer at the Tyson Food's poultry processing plant in Berlin, MD.

Water

FIGURE 5.13 Spiraling wastewater treatment in the Ocean Arks' lake restorer at the Tyson Food's poultry processing plant in Berlin, MD.

Suspension feeding bivalves also have been used as a form of bioremediation to control phytoplankton and, therefore, eutrophication of aquatic ecosystems. The filtration of the water column by bivalves during feeding removes phytoplankton and reduces turbidity. Nutrients are transferred from the pelagic zone to the benthos either by biodeposition in feces or psuedofeces (materials which are ingested but quickly rejected) or by incorporation into bivalve biomass. This approach has been shown to be effective for natural reefs of oysters (especially Crassostrea virginica) and beds of mussels. Officer et al. (1982) provide quantitative relationships showing criteria under which bivalves can control phytoplankton, based on prey-predator equations. Reviews are given by Dame (1996, 2001), Levinton et al. (2001), and Strayer et al. (1999). It has been further suggested that bivalves can be used, through a form of biomanipulation (see Chapter 7), to actively control eutrophication. Thus, Ulanowicz and Tuttle (1992) showed with a simulation model that oyster reef restoration and raft culture could significantly impact eutrophication in the Chesapeake Bay, and Wisniewski (1990) experimentally demonstrated techniques for enhancing zebra mussel (Dreissena polymorpha) filtration with artificial substrates in Poland. Raft culture in particular has been shown to have very high production rates of shellfish for food (Ryther, 1969), and therefore, it has potential for use in eutrophication control. Other suspension feeders, such as sponges on coral reefs (Diaz and Rutzler, 2001), along with polychaetes (families Sabellariidae and Ser-pulidae) and gastropods (family Vermetidae) that form reefs in tropical estuaries (Mohan and Aruna, 1994; Pandolfi et al., 1998; Schiaparelli and Cattaneo-Vietti, 1999), have high filtration rates and may be candidates for future ecological engineering design for bioremediation.

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