Continental Soil Salinity & Hydrological Vulnerability: Ancient Subsoil Palaeo-Salts Vs. Tigris-Euphrates Siltation

1. The Geochemical Crucible of Subsoil Palaeo-Salts across the Yilgarn Craton

The geological substrate of south-western Western Australia conceals one of the largest reservoirs of naturally occurring subsoil salt on the planet.^[1][6] Over millions of years of subaerial weathering, oceanic aerosols blown inland from the Southern and Indian Oceans deposited microscopic quantities of sodium chloride ($NaCl$) and magnesium salts across the Yilgarn Craton.^[1][6]

Because the landscape is exceptionally flat with negligible tectonic uplift, rainfall was insufficient to flush these salts to the sea.^[6] Consequently, cyclic salts accumulated in the deep regolith and weathered saprolite clay horizons, stored safely beneath the surface at concentrations ranging from 2,000 to over 10,000 tons of salt per hectare.^[1][6]

2. Deep-Rooted Perennial Hydrology: The Bibbullmun Equilibrium

For sixty thousand years, the Bibbullmun Sovereign Nation maintained this vast subterranean salt reservoir in complete hydrological equilibrium.^[1][2] The mechanism that prevented this ancient salt from rising to the surface was the continuous canopy of deep-rooted native perennial vegetation: Jarrah (Eucalyptus marginata), Marri (Corymbia calophylla), Wandoo (Eucalyptus wandoo), and Balga (Xanthorrhoea preissii).^[1][6]

These native plants possess deep taproots penetrating up to 20 to 40 meters into the fractured granitic bedrock, functioning as natural biological water pumps.^[1][6] Through high transpiration rates, the native forest consumed virtually 100% of annual rainfall, keeping the subterranean water table 15 to 30 meters below the surface.^[6] Under Bibbullmun custodial management, yam harvesting (wanna) and fire silviculture (Karl) were non-inversive: harvesting targeted surface geophytes while leaving deep tree roots and soil mycorrhizae completely intact, ensuring that the water table never rose.^[2][4]

3. The Colonial Ecological Disaster: Dryland Salinity and Soil Destruction

When European colonisers invaded, they brought an aggressive agricultural ideology developed on young, fertile, glaciated European soils (YODFELs), completely failing to comprehend the fragile geochemistry of the ancient Yilgarn Craton.^[1][3]

Between 1900 and 1970, colonial governments enforced mandatory land-clearing laws, bulldozing and chaining over 18 million hectares of native perennial forest to create the modern Western Australian Wheatbelt.^[1][6] The ecological consequence was catastrophic: without deep-rooted trees to transpire rainfall, groundwater recharge increased by more than ten-fold.^[6] The subterranean water table rose rapidly, dissolving millions of tons of ancient subsoil salts and carrying them directly into topsoils and river channels.^[1][6] Over 1.5 million hectares of productive farmland have been rendered sterile, toxic salt wastelands, while major rivers (such as the Avon and Blackwood) have been transformed into saline drains.^[1][6]

4. Tigris-Euphrates Parallels and First Nations Hydrological Sovereignty

The ecological collapse of the Western Australian Wheatbelt mirrors the ancient agricultural collapse of the Tigris-Euphrates River valley in ancient Mesopotamia, where intensive canal irrigation mobilized subsoil salts and doomed Sumerian civilisation.^[1][6]

The profound historical lesson is that the Bibbullmun people understood the hydrological vulnerability of their Country tens of thousands of years before modern soil science existed.^[1][2] By deliberately choosing not to practice deep mechanical soil inversion, Bibbullmun law protected the largest cratonic soil reservoir on Earth.^[1][2] The restoration of south-western hydrology requires the decolonization of landscape management and the complete restoration of Indigenous ecological sovereignty.^[1][6]