during the 1980s, information about the full range of ecosystem effects of acid rain is lacking for nearly all groups of aquatic organisms other than commercially important fish. Therefore, it still is not possible to predict with great accuracy the long-term consequences for the functioning of aquatic ecosystems of the alterations brought about by acid stress, and further research is needed.
Studies by paleolimnologists show that many ecosystems have not come to equilibrium with the acid loading now affecting them (Charles et al., 1990). Limnologists have also shown that climatic warming and acid deposition may have synergistic effects (Bayley et al., 1992a; Lazerte, 1993; Schindler et al., in press, b). Therefore, ecological and biogeochemical responses induced by acid rain can be revealed only by whole-ecosystem experiments and long-term studies over several decades. Too few such studies have been carried out, and more are needed in different terrains with differing biotic communities.
Now that many, but by no means all, countries have passed legislation to partially control emissions of sulfur, the continuation of studies of ecological effects of acid rain has been curtailed severely, as have studies of the recovery of ecosystems damaged by acid deposition. For example, research funds to study acidification problems have plummeted in the