Acidity from development of acid sulphate soils can be a major problem (Cook et al. 2000a and references therein) although the details of its impact on invertebrate communities are largely undocumented (see below). Development of these soils, which usually occur in low-lying coastal areas, can result in acid discharges when soil disturbance or drainage leads to oxidation of the pyrite in the soil. The resultant acidity of surface waters is often around pH 4 but can be as low as pH 2; in comparison, pH 6 is the minimum tolerated by most aquatic life. Acid discharges into river systems, estuaries and coastal waters have resulted in massive fish kills. Acid water also affects the health of fish and other aquatic life through damage to the skin and gills. Skin damage increases the susceptibility of fish to fungal infections that may lead to diseases such as epizootic ulcerative syndrome, also known as ‘red spot’. Gill and skin damage reduce the ability of organisms to take in oxygen or regulate their intake of salts and water (Sammut and Lines-Kelly 1996). Although the effects on marine invertebrates are far less well documented than those on fish, effects on some crustaceans[119], molluscs[120] and polychaetes[121] have been recorded. Undoubtedly other taxa are similarly affected. The aluminium in acid water also is toxic to most aquatic organisms because it damages their gills and at lethal levels can suffocate them. Wilson and Hyne (1997) found acid-sulphate soil leachate to be toxic to embryos of the Sydney Rock Oyster, with concentrations as low as 3.3% soil leachate in seawater decreasing normal development of the embryos after 48 hrs exposure; aluminium appeared to be the main toxicant. Sulphuric acid can also dissolve heavy metals in the soil such as cadmium, which when washed into waterways can be absorbed by fish and other aquatic life (Sammut and Lines-Kelly 1996; Cook et al. 2000b).

 

Sammut and Lines-Kelly (1996) summarised the short term and long term effects of acid water on fish and fish habitat (and by extrapolation, therefore, on invertebrates and their habitat) as:

 

Short term:

  • Fish kills, disease and destruction of eggs;

  • Mass mortalities of microscopic organisms;

  • Increased light penetration due to water clarity; and

  • Loss of acid-sensitive crustaceans; and

Long term:

  • Loss of habitat;

  • Persistent iron coatings;

  • Alterations to aquatic plant communities, including invasion of acid-tolerant taxa

  • Reduced spawning success due to stress and damaged and undeveloped eggs;

  • Chemical migration barriers;

  • Reduced food resources;

  • Dominance of acid-tolerant plankton species;

  • Growth abnormalities and reduced growth rates;

  • Increased predation and other changes in food chain and web;

  • Reduced recruitment;

  • Higher water temperatures due to increased light penetration;

  • Increased availability of toxic elements; and

  • Reduced availability of nutrients.

There are relatively few studies on the effects of acid soil leachate on marine or estuarine invertebrate communities. The effects of acid water inflow on estuarine benthic (and fish) communities in the Richmond River, NSW, were studied by Roach (1997). He found that changes to benthic communities in the lower estuary were evident following rainfall (which resulted in acid water inflow through numerous flood mitigation drains), but the magnitude of any change varied among acid-affected sites, and when compared to changes resulting from the inflow of freshwater alone, were relatively subtle (Roach 1997). However, the picture may have been complicated by the effects of chronic acid inflow. The major activity on potential acid sulphate soils is agriculture, especially sugar cane (Hogarth 1998).

 

In NSW, a three-year research project is being funded by the Fisheries Research and Development Corporation (FRDC) and NSW Fisheries, with the aim of developing guidelines to better manage floodgates (particularly in acid sulphate soil catchments), in order to improve water quality, as well as passage of fish and invertebrates (F. Kroon pers. comm.).



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Department of Environment and Heritage