The previous examples illustrate clearly the importance of studying functional couplings among aquatic ecosystems as well as to the surrounding uplands; without such studies, our understanding would be seriously inadequate. The nature of various problems of environmental degradation, many of which affect all upland and aquatic ecosystems in one way or another, provides a further and extremely cogent reason for such interecosystem studies, as shown by the following examples:
Example 1. If as expected, climate warming becomes a serious environmental problem in the next century (Intergovernmental Panel on Climate Change, Working Group 1, 1992), the Great Plains of North America will likely see a sharp decline in the number of prairie potholes combining wetlands suitable for the breeding of ducks with open water suitable for their feeding. Interpreting changes in these prairie potholes and in their associated biota as they dry out owing to greatly increased drought frequency will require a careful assessment of the linkages among lakes, ponds, and wetlands as they are affected in differing degrees by alterations in ground water hydrology. The prospect for devastating effects on duck populations in the Great Plains—already threatened by human overexploitation—is alarming.
Example 2. Studies of lake acidification ignored for a long time the possibility that upstream and marginal peatlands can be a potent source of acid inputs; these studies ascribed lake acidification solely to atmospheric deposition of sulfuric and nitric acids derived from air pollutants. Organic acids from peat bogs (Gorham et al., 1985) have, however, proved to be significant and, in some cases, predominant contributors to lake acidification in areas of Nova Scotia (Gorham et al., 1986; Kerekes et al., 1986; Gorham et al., in review), Norway (Brakke et al., 1987), and Finland (Kortelainen, 1993b). They must, therefore, be taken into account in much of the north temperate zone, where bogs are common features of the landscape. On the one hand, ignoring such natural acid inputs may overemphasize the effects of acid rain caused by human activity, but on the other hand, natural acidification of this kind may predispose some aquatic ecosystems to damage by relatively small inputs of acid rain.1
Example 3. Peats have a great capacity to bind toxaphene and DDT (Rapaport and Eisenreich, 1986), as well as other organochlorine micropollutants. The possibility exists, therefore, that wetlands—by their effective trapping of such materials—are a significant factor in lessening the
It should be noted that some clear water lakes on rocks that are not readily weathered can become quite acid through a variety of natural processes (Ford, 1990), though not to the degree brought about by acidic deposition from the atmosphere (Renberg, 1990) or substantial inputs from peat bogs in the catchment (Gorham et al., 1986).