Introduction

The devastating effects of acid precipitation (resulting from the conversion of atmospheric oxides of sulphur (SO2) and nitrogen (NOX) to sulphuric and nitric acid), on lake fauna and flora have been well documented (Likens & Borman, 1974; Leivestadt et al., 1976; Harvey & Lee, 1982). Losses of freshwater fish populations from such affected areas have been recorded (see, for example, Leivestadt & Muniz, 1976; Harvey, 1979, 1982) and possibly because of their great economic value many physiological studies have concentrated on the effects of acid exposure on fish (reviews by Wood & McDonald, 1982; McDonald, 1983; Wood, this volume). Decreases in invertebrate populations have also been reported (Abrahamsson, 1972; Aimer et al., 1974; France, 1983, 1985), but this has stimulated rather few studies on physiological disturbances resulting from acid exposure in invertebrate animals. Interestingly, the few studies which have been undertaken have shown invertebrates to be more tolerant to acid exposure than fish, or more accurately, than those few, mostly salmonid, fish on which physiological studies have concentrated.

A second common feature of the fish studies is that they have mostly used sulphuric acid (H2SO4) as the acid stressor. While H2SO4 precipitation still remains a most serious problem, in recent years emission of SO2 have declined while those of NOX have continued to rise. Despite this, few studies of the physiological effects of nitric acid (HNO3) pollution on aquatic animals have been carried out.