Environmental aspects of acid sulphate soils - ROOT of content

stream sites. Falls in pH at mainstream sites may also occur. For example, on theRichmond River in May 1987 at Site 4 (Figure 2), dissolved oxygen concentrationsfell from 5.8 mg I-' to 3.3 mg I-' and pH fell from 7.2 to 5.6 within 9 days of a majorrain event. However, at Site 4 in April 1988, dissolved oxygen concentrations fell from5.0 mg 1-' to 1.2 mg I-' but pH fell only marginally, from 6.6 to 6.2, within 10 daysof a major rain event.Clearly, runoff or drainage from acid sulphate soil areas contributes to thesechanges, to an extent dependent on a complex of factors including rainfall patternspreceding the major rain event and the distribution of rainfall over the catchmentduring the major rain event. However, it is likely that a 'pulse' of acidic, deoxygenatedwater is discharged from these areas during the early stages of most major rain events.Experimental exposure of fish to water with low pH (Daye & Garside 1976, Linnenbachet al 1987) and high aluminum concentrations (Tngersoll et al 1990b, Tandjunget al 1982) results in alterations to epidermal structure and, in extreme cases, epidermalnecrosis. Low concentrations of dissolved oxygen may also injure fish epidermis.Plumb et al (1 976) described apparantly sterile haemorrhagic and necrotic lesions inskin and skeletal muscle of channel catfish Ictalurus punctatus, exposed to dissolvedoxygen concentrations of less than 1 mg I-' for several days. They suggested that thisepidermal damage allowed subsequent bacterial invasion and septicaemia. It is likelythat, in some sections of lower river systems, and for varying periods after major rainevents, 'first-flush' runoff water from acid sulphate soil areas causes sublethal waterFigure 2 Location on the lower Richmond River of mainstream sampling sites for EUS prevalence (1-14)and known areas of acid sulphate soils (A-D)407