Environmental aspects of acid sulphate soils - ROOT of content

Seasonally recurrent fish mortalities andulcerative disease outbreaks associated withacid sulphate soils in Australian estuariesR.B. Callinan', G.C. Fraser' and M.D. Melville2NSW Fisheries, Regional Veterinary Laboratory, Wollongbar AustraliaSchool of Geography, University of NSW, Kensington, AustraliaAbstractAcid sulphate and potential acid sulphate soils are now known to be widespread onthe coasts of Australia, particularly in northern and eastern areas. The onset of heavyrain in these areas causes a 'first-flush' runoff and drainage of phytotoxic water withproperties including low pH and high concentrations of dissolved aluminum. Thesewaters have caused massive fish kills. Recently, a new ulcerative fish disease, epizooticulcerative syndrome (EUS), has shown a pattern of seasonal recurrence in EasternAustralia also relating to these onset rains. However, the pattern of this disease'sspread through Australia and Southeast Asia strongly suggests involvement of an exoticinfectious agent. The oomycete'fungus, Aphanomyces sp. has been consistently isolatedfrom ulcers but it is unable to invade the intact skin of healthy fish. Early indicationssuggest that chemical properties associated with water draining from acidsulphate soil areas cause sublethal skin damage that can allow fungal invasion. Thereis a clear spatial and temporal association between onset rains, drainage from acidsulphate soil areas and outbreaks of EUS, although the details of the disease processhave yet to be established.This disease threatens a major protein resource for human consumption in the Asia-Pacific region, where population growth pressure and need for economic developmentare great.Our ongoing research intends to establish, through field and laboratory studies,the role of water quality and hydrological parameters in the pathogenesis of EUS.This will allow better management of acid sulphate soil areas, thereby enhancing sustainabilityof estuarine fisheries.IntroductionAcid sulphate soils and potential acid sulphate soils are widely distributed in tidalriver flood plains in eastern and northern Australia. The sulphidic layers in these soilsacidify periodically under natural conditions, as in prolonged periods of dry weather,or following changes to flood plain hydrology, when backswamps and freshwaterlagoons are drainend by natural processes or human intervention.Recent studies in Australia have demonstrated probable causal relationships betweenmajor rain events, the presence of significant areas of acid sulphate soil in riverfloodplains and certain seasonally recurrent fish mortalities. Studies of epizootic ulcerativesydrome (EUS), a new disease of freshwater and estuarine fish in Australia, have403