Environmental aspects of acid sulphate soils - ROOT of content

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Table 1 Prevalence of EUS in yellowfin bream (Acanthopagrus uusrrulis) and sand whiting (SiNago ciliuia)sampled at 14 mainstream sites on the Richmond River at 3-monthly intervals on 7 occasions during1988j89. Location of sites is shown in Figure 2Site Yellowfin Bream Sand WhitingTotal No. with Prevalence Total No. with Prevalenceexamined EUS % examined EUS Yo12345678910II12131427 114232019101561996380019433422022331157618123 I227I73216268813322OO2.212.711.422.427.922.43.24.12.45.914.36.4OO-34.845.042.534.331.0-------quality changes in tributaries and some mainstream sites. Epidermal structuralchanges may occur in exposed fish. Such changes may act in a manner similar to experimentalabrasion and allow invasion by Aphanomyces sp. propagules, leading to developmentof typical EUS lesions.The hypothesis that runoff or drainage from acid sulphate soil areas has a causalrelationship to EUS is supported by the findings of a survey in which EUS prevalencein two relatively sedentary estuarine fish species, sand whiting (Silfugo ciliata) andyellowfin bream (Acanthopagrus australis), was measured at 3-monthly intervals, on7 occasions, at specific mainstream sites on the Richmond River during 1988/89. Findingsof the survey are summarised in Table 1.There are several acid sulphate soil sites in the lower Richmond River floodplain;the total distribution of such areas remains to be determined. EUS prevalence in yellowfinbream was highest in the section of river between Sites 2 and 6, where thecumulative effects of run-off from known acid sulphate soil areas should be at theirgreatest (Figure 2). Prevalence in this river section was also high in sand whiting, whichhave a more restricted distribution in the estuary. Given that the species examinedare relatively sedentary, it is likely that the EUS lesions were induced at these sites.At Site 1, buffering and dilution with sea water during tidal exchanges would occur,and it is noteworthy that EUS prevalence at this site was low.A similar association between EUS outbreaks and acid sulphate soils has been notedat a coastal study site in the Philippines (Reantaso, Paclibare, Callinan and Singh,unpublished). Acid soils, including acid sulphate soils, are widespread in Southeastand South Asia and may play a similar role in EUS induction in those regions. Studiesin Southeast Asia have associated EUS outbreaks with water having low hardness(the characteristic of water which represents the total concentrations of calcium andmagnesium expressed as calcium carbonate equivalent), low alkalinity (the buffering408
capacity of water expressed as calcium carbonate equivalent) and fluctuating pH(Anon 1989, Anon 1990a, Phillips 1992). Fish exposed to these conditions are highlysusceptible to injuries caused by low pH and toxic metal ions (Anon 1990b).ConclusionsWhile there is a clear causal association between fish kills and ‘first-flush’ run-offwater from acid sulphate soil areas in some Australian estuaries, a similar causal associationfor EUS remains to be established. There is, however, experimental evidencethat water quality attributes such as low pH, high concentrations of inorganic aluminumand,low concentrations of dissolved oxygen which are present in this ‘first-flush’water, may injure skin of sub-lethally exposed fish; the putative infectious cause ofEUS, an Aphanomyces fungus, may then be able to invade these damaged areas andproduce the characteristic ulcers.In view of the potential of seasonally recurrent EUS outbreaks, as well as fish kills,to cause long-term damage to the sustainability of estuarine fisheries in the Asia-Pacificregion, it is essential that major causal factors are identified and appropriate controlmeasures, such as ameliorative drainage management practices, are put in place. However,given the complex interactions between rain events, acid sulphate soil areas, riverflow patterns, populations of susceptible fish and distribution of the pathogenic Aphanomycessp., considerable research effort will be required to elucidate thoroughly thepossible relationships.AcknowledgementsWe thank R. West and G. McLennan for kind permission to include EUS prevalencedata and water quality data respectively. We also thank C. Peak for generously assistingin the preparation of figures and A. Parrington for typing the manuscript. Thesestudies were funded, in part, by Land and Water Resources Research and DevelopmentCorporation.ReferencesAnon 1989. A report on the NACA workshop on the regional research program on ulcerative syndromein fish and the environment. Network of Aquaculture Centres in Asia-Pacific, BangkokAnon 1990a. Regional research program on relationships between epizootic ulcerative syndrome in fishand the environment. Network of Aquaculture Centres in Asia-Pacific, BangkokAnon 1990b. Water quality management for aquaculture and fisheries. Institute of Aquaculture, Universityof Stirling, ScotlandAnon 1991. Fish health management in Asia-Pacific. Report on a regional study and workshop on fishdisease and fish health management. Asian Development Bank Agriculture Department Report SeriesNo. I, Network of Aquaculture Centres in Asia-Pacific, BangkokBirchall, J.D., C. Exley, J.S. Chappell and M.J. Phillips 1989. Acute toxicity ofaluminum to fish eliminatedin silicon-rich acid waters. Nature 338, 146-148Brown, D.J. 1983. Effect of calcium and aluminum concentrations on the survival of brown trout (Salmotrutta) at low pH. Bulletin of Environmental Contamination and Toxicology 30, 582-587409
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