All sewage and many industrial waste-treatment plants depend heavily on biological processes, although one might not reach this conclusion from examination of an operator’s training manual. However, the ecological distance between the waste-treatment plant and natural ecosystems is too great. A gnotobiotic system designed to act as an ecological buffer between the two systems should help increase diversity in the natural system by more efficiently carrying out processes not completed by the waste-treatment system for which the natural system is not well equipped. Since most waste-treatment plants are not located in pristine ecological environments, these ecological buffers would be constructed on damaged or partly damaged ecosystems.
The selection of species for these assemblages should be based on their tolerance for the waste and on their ability to carry out the remaining transformation processes. They might or might not occur naturally together. The only contaminants one can easily process in this way are those from point sources. However, by appropriate design of run-off collection systems, nonpoint discharges, such as agricultural wastes and surface mine wastes, can be converted to point source discharges. Since most of these contaminants are waterborne, artificial wetlands are probably the best buffer ecosystems for coping with them. Such systems can tolerate heavy loadings of both organic wastes and some toxicants. Recent descriptions may be found in Brooks et al. (1985).
There is persuasive evidence of groundwater contamination in North America, but its extent has not been well defined. There seems to be little concern about the fate of the organisms that inhabit the aquifers, however, even though they occupy a unique habitat and are part of the global diversity. Some of the contaminated aquifers might be partly decontaminated by the introduction of engineered microorganisms to degrade the wastes. Although presumably less dangerous, the water would not yet be normal. In some cases, quality could be further improved by pumping the water to the surface and passing it through an artificial wetland before recharge through a pipe or by normal infiltration.
The many contaminated and depleted aquifers could be recharged by artificial wetlands designed for this purpose. These can be built on damaged ecosystems, as Brooks et al. (1985) have shown.
Damaged ecosystems can be changed from ecological liabilities to assets that are useful in both increasing diversity and protecting natural systems in a variety of ways. They can be developed as ecological buffers between waste-treatment systems and natural systems. Damaged ecosystems can be used to replace wetlands and other scarce habitats lost to development, even when such habitats did not originally exist on the damaged site. They can be developed as refuges for rare, en-