buildup of such toxic pollutants in downstream ecosystems. If severe climate warming comes to pass and leads to drawdown of peatland water tables, it may well be that subsequent peat aeration and oxidation will release these toxins—largely concentrated in the surface peats—downstream. The same may be true of nitrogen and sulfur, stored in these peatlands in large amounts (Gorham, 1994) and liable to be released in acid form by drought and fire (Bayley et al., 1992). Bog mosses and lichens also have a strong affinity for radioactive fallout (Gorham, 1958, 1959; Miettinen, 1969), which could be released similarly. In all three cases there is the potential for ecological damage, but at present we lack sufficient information to evaluate its likely significance.

Example 4. Oil pollution is a largely local problem in all sorts of ecosystems from the uplands to the ocean. Many different organisms from diverse habitats are capable of degrading different petroleum compounds (Freedman, 1989b). The search for the most efficient among them for use in bioremediation should encompass the full range of those habitats.

In all of these examples, restriction of studies to a single type of ecosystem would also restrict, to a very significant extent, both our thinking about and our understanding of serious environmental problems.

IMPORTANT QUESTIONS FOR FUTURE RESEARCH ON THE LINKAGES AMONG AQUATIC ECOSYSTEMS

More attention to interecosystem linkages can be justified only if truly important research questions, both fundamental and practical, can be asked about them. The following are a few examples suggested from experience in studying lakes, streams, and wetlands. Individual scientists will be able to add their own examples, and environmental surprises in the years to come will reveal many more cases in which a better understanding of interecosystem linkages would have served us well.

Example 1. How does the influence of organic carbon compounds (both particulate and dissolved) on (1) aquatic productivity; (2) acid-base balance; (3) oxidation-reduction potential; (4) trace-metal transport; and (5) emissions of volatile carbon, nitrogen, and sulfur compounds change from the time of its deposition as dead organic matter (forest litter and aquatic plant remains) to the time of its ultimate arrival in the open ocean, having passed through streams, wetlands, small and large lakes, large rivers, and estuaries? All of these items are important elements in the metabolism of aquatic ecosystems, on which sport and commercial fisheries depend, but although we have fitted some parts of the metabolic puzzle together we do not yet have anything close to a complete picture spanning the full range of aquatic ecosystems.

Example 2. Do chemical inputs of nutrients and toxins from wetlands have an influence on the biodiversity of receiving streams and lakes? It



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