Acid sulfate soil
Encyclopedia
Acid sulfate soils are naturally occurring soils, sediments or organic substrates (e.g. peat
) that are formed under waterlogged conditions. These soils contain iron sulfide
minerals (predominantly as the mineral pyrite
) or their oxidation
products. In an undisturbed state below the water table, acid sulfate soils are benign. However if the soils are drained, excavated or exposed to air by a lowering of the water table, the sulfides react with oxygen
to form sulfuric acid
.
Release of this sulfuric acid from the soil can in turn release iron
, aluminium
, and other heavy metals
(particularly arsenic
) within the soil. Once mobilized in this way, the acid and metals can create a variety of adverse impacts: killing vegetation, seeping into and acidifying groundwater
and water bodies, killing fish
and other aquatic organisms, and degrading concrete
and steel
structures to the point of failure.
conditions, lithotrophic bacteria such as Desulfovibrio desulfuricans
obtain oxygen for respiration though the reduction of sulfate ions in sea or groundwater, producing hydrogen sulfide. This in turn reacts with dissolved ferrous iron, forming very fine grained and highly reactive framboid
crystals of iron sulfides such as (pyrite
). Up to a point, warmer temperatures are more favourable conditions for these bacteria, creating a greater potential for formation of iron sulfides. Tropical waterlogged environments, such as mangrove
swamps or estuaries, may contain higher levels of pyrite than those formed in more temperate climates.
The pyrite is stable until exposed to air, at which point the pyrite rapidly oxidises and produces sulfuric acid. The impacts of acid sulfate soil leachate may persist over a long time, and/or peak seasonally (after dry periods with the first rains). In some areas of Australia, acid sulfate soils that drained 100 years ago are still releasing acid.
< 4) due to the oxidation of pyrite into sulfuric acid (H2SO4). In its simplest form, this chemical reaction
is as follows:
The product Fe(OH)3, iron(III) hydroxide (orange), precipitates as 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:
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, whereas the ferric form is not. 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.
sulfate-rich groundwater in some agricultural areas. In Australia, coastal acid sulfate soils occupy an estimated 80,000 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.
Acid sulfate soils that have not been disturbed are called potential acid sulfate soils (PASS). Acid sulfate soils that have been disturbed are called actual acid sulfate soils (AASS).
s. Flushing of acidic leachate
to groundwater and surface waters can cause a number of impacts, including:
, so that the soil can be kept wet preventing oxidation. Subsurface drainage
of these soils is normally not advisable.
When cultivated, acid sulfate soils cannot be kept wet continuously because of climatic dry spells and shortages of irrigation
water, surface drainage may help to remove the acidic and toxic chemicals (formed in the dry spells) during rainy periods. In the long run surface drainage can help to reclaim acid sulfate soils. The indigenous population of Guinea Bissau has thus managed to develop the soils, but it has taken them many years of careful management and toil.
In an article on cautious land drainage, the author describes the successful application of subsurface drainage in acid sulfate soils in coastal polders of Kerala state, India.
Also in the Sunderbans, West Bengal, India, acid sulfate soils have been taken in agricultural use.
A study in South Kalimantan
, Indonesia, in a perhumid climate, has shown that the acid sulfate soils with a widely spaced subsurface drainage system have yielded promising results for the cultivation of upland (sic!) rice
, peanut
and soybean
. The local population, of old, had already settled in this area and were able to produce a variety of crops (including tree fruits), using hand-dug drains running from the river into the land until reaching the back swamps. The crop yields were modest, but provided enough income to make a decent living.
Reclaimed acid sulfate soils have a well-developed soil structure
; they are well permeable, but infertile due to the leaching
that has occurred.
In the second half of the 20th century, in many parts of the world, waterlogged
and potentially acid sulfate soils have been drained aggressively to make them productive for agriculture
. The results were disastrous. The soils are unproductive, the lands look barren and the water is very clear, devoid of silt and life. The soils can be colorful, though.
. To identify the pH level of the ground a soil investigation must take place.
The following table gives an example.
Drainage and yield of Malaysian oil palm on acid sulfate soils (after Toh Peng Yin and Poon Yew Chin, 1982)
Yield in tons of fresh fruit per ha:
Drainage depth and intensity were increased in 1962. The water table was raised again in 1966 to counter negative effects.
Peat
Peat is an accumulation of partially decayed vegetation matter or histosol. Peat forms in wetland bogs, moors, muskegs, pocosins, mires, and peat swamp forests. Peat is harvested as an important source of fuel in certain parts of the world...
) that are formed under waterlogged conditions. These soils contain iron sulfide
Iron sulfide
Iron sulfide or Iron sulphide refers to a chemical compound of iron and sulfur with a wide range of stoechiometric formulae and different crystalline structures.-Natural minerals:By increasing order of stability:...
minerals (predominantly as the mineral pyrite
Pyrite
The mineral pyrite, or iron pyrite, is an iron sulfide with the formula FeS2. This mineral's metallic luster and pale-to-normal, brass-yellow hue have earned it the nickname fool's gold because of its resemblance to gold...
) or their oxidation
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
products. In an undisturbed state below the water table, acid sulfate soils are benign. However if the soils are drained, excavated or exposed to air by a lowering of the water table, the sulfides react with oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
to form sulfuric acid
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...
.
Release of this sulfuric acid from the soil can in turn release iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
, aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
, and other heavy metals
Heavy metals
A heavy metal is a member of a loosely-defined subset of elements that exhibit metallic properties. It mainly includes the transition metals, some metalloids, lanthanides, and actinides. Many different definitions have been proposed—some based on density, some on atomic number or atomic weight,...
(particularly arsenic
Arsenic
Arsenic is a chemical element with the symbol As, atomic number 33 and relative atomic mass 74.92. Arsenic occurs in many minerals, usually in conjunction with sulfur and metals, and also as a pure elemental crystal. It was first documented by Albertus Magnus in 1250.Arsenic is a metalloid...
) within the soil. Once mobilized in this way, the acid and metals can create a variety of adverse impacts: killing vegetation, seeping into and acidifying groundwater
Groundwater
Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock...
and water bodies, killing fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
and other aquatic organisms, and degrading concrete
Concrete
Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...
and steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
structures to the point of failure.
Acid sulfate soil formation
The soils and sediments most prone to becoming acid sulfate soils formed within the last 10,000 years, after the last major sea level rise. When the sea level rose and inundated the land, sulfate in the seawater mixed with land sediments containing iron oxides and organic matter. Under these anaerobicHypoxia (environmental)
Hypoxia, or oxygen depletion, is a phenomenon that occurs in aquatic environments as dissolved oxygen becomes reduced in concentration to a point where it becomes detrimental to aquatic organisms living in the system...
conditions, lithotrophic bacteria such as Desulfovibrio desulfuricans
Desulfovibrio
Desulfovibrio is a genus of Gram negative sulfate-reducing bacteria. Some species of Desulfovibrio are capable of transduction. Desulfovibrio species are commonly found in aquatic environments with high levels of organic material, as well as in water-logged soils, and form major community members...
obtain oxygen for respiration though the reduction of sulfate ions in sea or groundwater, producing hydrogen sulfide. This in turn reacts with dissolved ferrous iron, forming very fine grained and highly reactive framboid
Framboid
The term framboid describes a micromorphological feature common to certain sedimentary minerals, particularly pyrite . The first known use of the term is ascribed to Rust in 1935 and is derived from the French ‘la framboise’, meaning ‘raspberry’, reflecting the appearance of the structure under...
crystals of iron sulfides such as (pyrite
Pyrite
The mineral pyrite, or iron pyrite, is an iron sulfide with the formula FeS2. This mineral's metallic luster and pale-to-normal, brass-yellow hue have earned it the nickname fool's gold because of its resemblance to gold...
). Up to a point, warmer temperatures are more favourable conditions for these bacteria, creating a greater potential for formation of iron sulfides. Tropical waterlogged environments, such as mangrove
Mangrove
Mangroves are various kinds of trees up to medium height and shrubs that grow in saline coastal sediment habitats in the tropics and subtropics – mainly between latitudes N and S...
swamps or estuaries, may contain higher levels of pyrite than those formed in more temperate climates.
The pyrite is stable until exposed to air, at which point the pyrite rapidly oxidises and produces sulfuric acid. The impacts of acid sulfate soil leachate may persist over a long time, and/or peak seasonally (after dry periods with the first rains). In some areas of Australia, acid sulfate soils that drained 100 years ago are still releasing acid.
Chemical reaction
When drained, pyrite (FeS2) containing soils (also called cat-clays) may become extremely acidic (pHPH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
< 4) due to the oxidation of pyrite into sulfuric acid (H2SO4). In its simplest form, this chemical reaction
Chemical reaction
A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity...
is as follows:
- 2 FeS2 + 9 O2 + 4 H2O → 8 H+ + 4 SO42− + 2 Fe(OH)3 (solid)
The product Fe(OH)3, iron(III) hydroxide (orange), precipitates as a solid, insoluble mineral by which the alkalinity
Alkalinity
Alkalinity or AT measures the ability of a solution to neutralize acids to the equivalence point of carbonate or bicarbonate. The alkalinity is equal to the stoichiometric sum of the bases in solution...
component is immobilized, while the acidity remains active in the sulfuric acid
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...
. The process of acidification is accompanied by the formation of high amounts of aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
(Al3+, released from clay minerals
Clay minerals
Clay minerals are hydrous aluminium phyllosilicates, sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations. Clays have structures similar to the micas and therefore form flat hexagonal sheets. Clay minerals are common weathering products and low...
under influence of the acidity), which are harmful to vegetation. Other products of the chemical reaction are:
- Hydrogen sulfideHydrogen sulfideHydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...
(H2S), a smelly gas - SulfurSulfurSulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
(S), a yellow solid - Iron(II) sulfideIron(II) sulfideIron sulfide or ferrous sulfide is a chemical compound with the formula . In practice, iron sulfides are often non-stoichiometric. Powdered iron sulfide is pyrophoric Iron(II) sulfide or ferrous sulfide (Br.E. sulphide) is a chemical compound with the formula . In practice, iron sulfides are...
(FeS), a black/gray/blue solid - Haematite (Fe2O3), a red solid
- GoethiteGoethiteGoethite , named after the German polymath Johann Wolfgang von Goethe, is an iron bearing oxide mineral found in soil and other low-temperature environments. Goethite has been well known since prehistoric times for its use as a pigment. Evidence has been found of its use in paint pigment samples...
(FeO.OH), a brown mineral - SchwertmanniteSchwertmanniteSchwertmannite is an iron-oxyhydroxysulfate mineral with an ideal chemical formula of 886·nH2Oor Fe3+16O1612-13·10-12H2O. It is an opaque tetragonal mineral typically occurring as brownish yellow encrustations...
a brown mineral - Iron sulfate compounds (e.g. jarositeJarositeJarosite is a basic hydrous sulfate of potassium and iron with a chemical formula of KFe3+362. This sulfate mineral is formed in ore deposits by the oxidation of iron sulfides...
) - H-Clay (hydrogenHydrogenHydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
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, whereas the ferric form is not. 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
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
(Mg) and sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
(Na) in the sea water replaces the adsorbed
Adsorption
Adsorption is the adhesion of atoms, ions, biomolecules or molecules of gas, liquid, or dissolved solids to a surface. This process creates a film of the adsorbate on the surface of the adsorbent. It differs from absorption, in which a fluid permeates or is dissolved by a liquid or solid...
hydrogen.
Geographical distribution
Acid sulfate soils are widespread around coastal regions, and are also locally associated with freshwater wetlands and salineSaline water
Saline water is a general term for water that contains a significant concentration of dissolved salts . The concentration is usually expressed in parts per million of salt....
sulfate-rich groundwater in some agricultural areas. In Australia, coastal acid sulfate soils occupy an estimated 80,000 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.
Acid sulfate soils that have not been disturbed are called potential acid sulfate soils (PASS). Acid sulfate soils that have been disturbed are called actual acid sulfate soils (AASS).
Impacts of acid sulfate soil
Disturbing potential acid sulfate soils can have a destructive effect on plant and fish life, and on aquatic ecosystemAquatic ecosystem
An aquatic ecosystem is an ecosystem in a body of water. Communities of organisms that are dependent on each other and on their environment live in aquatic ecosystems. The two main types of aquatic ecosystems are marine ecosystems and freshwater ecosystems....
s. Flushing of acidic leachate
Leachate
Leachate is any liquid that, in passing through matter, extracts solutes, suspended solids or any other component of the material through which it has passed....
to groundwater and surface waters can cause a number of impacts, including:
- Ecological damage to aquatic and riparian ecosystems through fish killFish killThe term fish kill, known also as fish die-off and as fish mortality, is a localized die-off of fish populations which may also be associated with more generalised mortality of aquatic life...
s, increased fish diseaseFish diseases and parasitesLike humans and other animals, fish suffer from diseases and parasites. Fish defences against disease are specific and non-specific. Non-specific defences include skin and scales, as well as the mucus layer secreted by the epidermis that traps microorganisms and inhibits their growth...
outbreaks, dominance of acid-tolerant species, precipitation of iron, etc. - Effects on estuarineEstuaryAn estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea....
fisheries and aquacultureAquacultureAquaculture, also known as aquafarming, is the farming of aquatic organisms such as fish, crustaceans, molluscs and aquatic plants. Aquaculture involves cultivating freshwater and saltwater populations under controlled conditions, and can be contrasted with commercial fishing, which is the...
projects (increased disease, loss of spawning area, etc.). - Contamination of groundwater with arsenicArsenicArsenic is a chemical element with the symbol As, atomic number 33 and relative atomic mass 74.92. Arsenic occurs in many minerals, usually in conjunction with sulfur and metals, and also as a pure elemental crystal. It was first documented by Albertus Magnus in 1250.Arsenic is a metalloid...
, aluminiumAluminiumAluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
and other heavy metals. - Reduction in agricultural productivity through metal contamination of soils (predominantly by aluminium).
- Damage to infrastructureInfrastructureInfrastructure is basic physical and organizational structures needed for the operation of a society or enterprise, or the services and facilities necessary for an economy to function...
through the corrosion of concrete and steel pipes, bridges and other sub-surface assets.
Agricultural impacts
Potentially acid sulfate soils (also called cat-clays) are often not cultivated or, if they are, planted under riceRice
Rice is the seed of the monocot plants Oryza sativa or Oryza glaberrima . As a cereal grain, it is the most important staple food for a large part of the world's human population, especially in East Asia, Southeast Asia, South Asia, the Middle East, and the West Indies...
, so that the soil can be kept wet preventing oxidation. Subsurface drainage
Drainage
Drainage is the natural or artificial removal of surface and sub-surface water from an area. Many agricultural soils need drainage to improve production or to manage water supplies.-Early history:...
of these soils is normally not advisable.
When cultivated, acid sulfate soils cannot be kept wet continuously because of climatic dry spells and shortages of irrigation
Irrigation
Irrigation may be defined as the science of artificial application of water to the land or soil. It is used to assist in the growing of agricultural crops, maintenance of landscapes, and revegetation of disturbed soils in dry areas and during periods of inadequate rainfall...
water, surface drainage may help to remove the acidic and toxic chemicals (formed in the dry spells) during rainy periods. In the long run surface drainage can help to reclaim acid sulfate soils. The indigenous population of Guinea Bissau has thus managed to develop the soils, but it has taken them many years of careful management and toil.
In an article on cautious land drainage, the author describes the successful application of subsurface drainage in acid sulfate soils in coastal polders of Kerala state, India.
Also in the Sunderbans, West Bengal, India, acid sulfate soils have been taken in agricultural use.
A study in South Kalimantan
Kalimantan
In English, the term Kalimantan refers to the Indonesian portion of the island of Borneo, while in Indonesian, the term "Kalimantan" refers to the whole island of Borneo....
, Indonesia, in a perhumid climate, has shown that the acid sulfate soils with a widely spaced subsurface drainage system have yielded promising results for the cultivation of upland (sic!) rice
Rice
Rice is the seed of the monocot plants Oryza sativa or Oryza glaberrima . As a cereal grain, it is the most important staple food for a large part of the world's human population, especially in East Asia, Southeast Asia, South Asia, the Middle East, and the West Indies...
, peanut
Peanut
The peanut, or groundnut , is a species in the legume or "bean" family , so it is not a nut. The peanut was probably first cultivated in the valleys of Peru. It is an annual herbaceous plant growing tall...
and soybean
Soybean
The soybean or soya bean is a species of legume native to East Asia, widely grown for its edible bean which has numerous uses...
. The local population, of old, had already settled in this area and were able to produce a variety of crops (including tree fruits), using hand-dug drains running from the river into the land until reaching the back swamps. The crop yields were modest, but provided enough income to make a decent living.
Reclaimed acid sulfate soils have a well-developed soil structure
Soil structure
Soil structure is determined by how individual soil granules clump or bind together and aggregate, and therefore, the arrangement of soil pores between them...
; they are well permeable, but infertile due to the leaching
Leaching (pedology)
In pedology, leaching is the loss of mineral and organic solutes due to percolation. It is a mechanism of soil formation. It is distinct from the soil forming process of eluviation, which is the loss of mineral and organic colloids. Leached and elluviated materials tend to be lost from topsoil and...
that has occurred.
In the second half of the 20th century, in many parts of the world, waterlogged
Waterlogging (agriculture)
Waterlogging refers to the saturation of soil with water. Soil may be regarded as waterlogged when the water table of the groundwater is too high to conveniently permit an anticipated activity, like agriculture....
and potentially acid sulfate soils have been drained aggressively to make them productive for agriculture
Agriculture
Agriculture is the cultivation of animals, plants, fungi and other life forms for food, fiber, and other products used to sustain life. Agriculture was the key implement in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that nurtured the...
. The results were disastrous. The soils are unproductive, the lands look barren and the water is very clear, devoid of silt and life. The soils can be colorful, though.
Construction
When brickwork is persistently wet, as in foundations, retaining walls, parapets and chimneys, sulfates in bricks and mortar may in time crystallise and expand and cause mortar and rederings to disintegrate. To minimise this effect specialised brickwork with low sulfate levels should be used. Acid sulfates that are located within the subsoil strata has the same effects on the foundations of a building. Adequate protection can exist using a polythene sheeting to encase the foundations or using a sulfate resistant Portland cementPortland cement
Portland cement is the most common type of cement in general use around the world because it is a basic ingredient of concrete, mortar, stucco and most non-specialty grout...
. To identify the pH level of the ground a soil investigation must take place.
Acid sulfate soil restoration
By raising the water table, after damage has been inflicted due to over-intensive drainage, the soils can be restored.The following table gives an example.
Drainage and yield of Malaysian oil palm on acid sulfate soils (after Toh Peng Yin and Poon Yew Chin, 1982)
Yield in tons of fresh fruit per ha:
| Year | 60 | 61 | 62 | 63 | 64 | 65 | 66 | 67 | 68 | 69 | 70 | 71 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Yield | 17 | 14 | 15 | 12 | 8 | 2 | 4 | 8 | 14 | 19 | 18 | 19 |
Drainage depth and intensity were increased in 1962. The water table was raised again in 1966 to counter negative effects.
Further reading
- Sammut, J., White, I. and Melville, M.D. (1996). Acidification of an estuarine tributary in eastern Australia due to drainage of acid sulfate soils. Marine and Freshwater Research 47, 669-684.
- Sammut, J., Melville, M.D., Callinan, R.B. and Fraser, G. (1995). Estuarine acidification: impacts on aquatic biota of draining acid sulphate soils. Australian Geographical Studies 33, 89-100.
- Wilson, B.P, White I. and Melville M.D. (1999). Floodplain hydrology, acid discharge and change in water quality associated with a drained acid sulfate soil. Marine and Freshwater Research. 50; 149-157.
- Wilson, B.P. (2005) Classification issues for the Hydrosol and Organosol Soil Orders to better encompass surface acidity and deep sulfidic horizons in acid sulfate soils. Australian Journal of Soil Research 43; 629-638
- Wilson, B.P. (2005) Elevations of pyritic layers in acid sulfate soils: what do they indicate about sea levels during the Holocene in eastern Australia. Catena 62; 45-56.
External links
- Australian Department of Environment & Heritage National Coastal Acid Sulfate Soil website
- Queensland Department of Natural Resources & Water Acid Sulfate Soils website
- Western Australian Department of Environment Acid Sulfate Soils website
- http://www.waterlog.info/faqs.htm Frequently asked questions, question 3: documentation on acid sulfate soils