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|Photographer: Cara Beal
Residue on the sandy shore of a tidal pool on North Stradbroke Island, Qld.
|Each time the tide ebbs it leaves a line of residue on the sand surface. The tannic residues left on this sand come from an upstream melaleuca wetland that drains into the tidal pool via surface and subsurface flows.|
|Photographer: Balwant Singh
Crystals of halite and gypsum formed in drying wetlands at Bottle Bend Lagoon near Mildura.
|The drying of the wetland has resulted in the incursion of saline groundwater (several times more saline than the seawater) and microbial oxidation of sulfides in the lagoon sediments resulting in pH<3. The mix of salinity and acidity has resulted in formation of salt efflorescences of needle-shaped crystals of halite (NaCl) with small amounts of gypsum (CaSO4.2H2O). The orange crust and gel on halite crystals is made up of akaganéite (β-FeOOH), a poorly crystalline iron oxyhydroxide mineral.|
|Photographer: Elise Wenden
Ant nests in a light sandy Calcarosol at Tutye South, Central Mallee, Victoria.
|Ants are the earthworms of arid environments. They incorporate organic matter on the soil surface into the soil (pedoturbation) and play an important role in distributing water. Their extensive underground nests are effectively macropores that enable water to enter the soil easily. The more entrances there are, the faster water can enter. The wider the entrances, the deeper the water penetrates into the soil.|
|Photographer: Justine Cox Macadamia tree roots in well structured Red Ferrosol soils on the Alstonville Plateau in northern NSW.||Exposed ferrosols are easily eroded, so in a region where torrential downpours funnel hundreds of litres of water down each macadamia tree trunk onto the soil, groundcovers and mulches are crucial.|
|Photographer: Janet Wild
A colourful carpet of autumn leaves at Wagga Wagga, NSW.
|Autumn leaves are part of the natural cycling of organic matter that protects the soil surface from erosion and breaks down to fertilise and renew the earth. The red colour is due to anthocyanin pigments produced by trees to protect the leaves while nutrients are recovered from the leaves before they fall. US research has found trees produce more anthocyanins where soils are relatively low in nitrogen and other essential elements.|
|Photographer: Kelly Bryant
Soil from a drying saline lake at Hungerford, southwest Queensland.
|This soil profile shows the white salt-encrusted surface layer over a greeny-grey gleyed layer. The gleyed colours occur because anaerobic microorganisms obtain their oxygen from mineral compounds in the waterlogged soil, and in the process reduce the oxygen content of the soil. When oxygen returns to the soil, iron in the soil oxidises and becomes orange-red, as can be seen along the root channels.|
|Photographer: Robert Banks
Eroded gully at Kenebri NSW, north of Coonabarabran
|The soil in this gully is a Brown Sodosol with a surface pH of about 5.0 and a B horizon pH of 9.5. It overlies up to five paeleosols, buried under sediment and volcanic layers. Parts of the bottom of the gully have debris from the original Warrumbungle Volcano explosions 17 million years ago. The bedrock is Jurassic Pilliga Sandstone which is exposed in some areas.|
|Photographer: Andrew Biggs
Bird footprints on the shore of Lake Wyara, part of the Currawinya Lakes RAMSAR wetlands in south-western Qld.
|The lakes are known for their waterbird breeding, and the softer soil (Sulfidic Hypersalic Hydrosol) on surfaces in the lower parts of the lake area is heavily trampled by birds. As the soil dries out, a salt crust forms, which eventually collapses. The polygonal cracking is a common feature of drying saline clays.|
|Photographer: Mark Imhof
Young crops on fertile volcanic soil (Ferrosol) near Leongatha, Victoria.
|Basalt-derived Ferrosols are highly prized for agricultural production because their physical structure allows plant roots, water and air to move easily through them. However, they need careful management and plenty of additional organic matter, otherwise they erode easily, leach nutrients, tie up phosphorus and become more acidic and much less productive.|
|Photographer: Paul Shand
Yellow crystals of sideronatrite on the surface of acid sulfate soils that were formerly covered in
fresh water at Poltalloch on the shores of Lake Alexandrina, South Australia.
|Sideronatrite [Na2Fe3+(SO4)2(OH)·3H2O] forms after the rapid oxidation and dissolution of pyrite crystals in acid sulfate soil. It is one of many complex minerals emerging in Australia’s drought-stricken inland where soils that had been covered in water for decades are now drying. It is relatively rare, as it only forms in extremely acid soils. Its name derives from the Greek words for iron (sideros) and sodium (natrium).|
|Photographer: Nathan Heath
Clay curls near Ouyen, Victoria.
|Many Australian soils are affected by socidity (exchangeable sodium percentage, ESP>6). Sodic clays are dispersive, and the evidence of this can be seen in cloudy dams full of suspended clay particles or in milky puddles after rain on bare soil. As a puddle or dam dries, the suspended particles collect in a layer on the surface of the soil or dam floor. As this layer dries, it shrinks and cracks into polygonal units. The upper surface of each unit dries faster than the underside, so each unit curls inward and away from the soil surface.|
|Photographer: Ian Packer
Inter-row sowing between wheat stubble in a Red Chromosol, near Cowra NSW.
|Retaining stubble in cropping paddocks builds organic matter in the soil, and helps prevent erosion. The cloddiness of this soil indicates low organic matter and structural decline from over-cultivation.|