a solid, insoluble mineral by which the alkalinity component is immobilized, while the acidity remains active in the sulfuric acid. The process of acidification is accompanied by the formation of high amounts of aluminium (Al3+, released from clay minerals under influence of the acidity), which are harmful to vegetation. Other products of the chemical reaction are: Hydrogen sulfide (H2S), a foul-smelling gas Sulfur (S), a yellow solid Iron(II) sulfide (FeS), a black/gray/blue solid Hematite (Fe2O3), a red solid Goethite (FeO.OH), a brown mineral Iron sulfate compounds (e.g., jarosite, schwertmannite, gypsum, and epsomite) H-Clay (hydrogen clay, with a large fraction of adsorbed H+ ions, a stable mineral, but poor in nutrients) The iron can be present in bivalent and trivalent forms (Fe2+, the ferrous ion, and Fe3+, the ferric ion respectively). The ferrous form is soluble in a relatively wide range of pH conditions whereas the ferric form is not soluble except in an extremely acidic environment such as muriatic acid rust remover. The more oxidized the soil becomes, the more the ferric forms dominate. Acid sulfate soils exhibit an array of colors ranging from black, brown, blue-gray, red, orange and yellow. The hydrogen clay can be improved by admitting sea water: the magnesium (Mg) and sodium (Na) in the sea water replaces the adsorbed hydrogen and other exchangeable acidic cations such as aluminium (Al). However this can create additional risks when the hydrogen ions and exchangeable metals are mobilised. Geographical distribution Acid sulfate soils are widespread around coastal regions, and are also locally associated with freshwater wetlands and saline sulfate-rich groundwater in some agricultural areas. In Australia, coastal acid sulfate soils occupy an estimated 58,000 km2, underlying coastal estuaries and floodplains near where the majority of the Australian population lives. Acid sulfate soil disturbance is often associated with dredging, excavation dewatering activities during canal, housing and marina developments. Droughts can also result in acid sulfate soil exposure and acidification. Impact Disturbing potential acid sulfate soils can have a destructive effect on plant and fish life, and on aquatic ecosystems. Flushing of acidic leachate to groundwater and surface waters can cause a number of impacts, including: Ecological damage to aquatic and riparian ecosystems through fish kills, increased fish disease outbreaks, dominance of acid-tolerant species, precipitation of iron, etc. Effects on estuarine fisheries and aquaculture projects (increased disease, loss of spawning area, etc.). Contamination of groundwater and surface water with arsenic, aluminium