White Sand/Yellow Sand

Have you noticed that we have golden sands on our beaches, but further inland the sand is often pure white? Scott Toohey, Environment Manager at Couran Cove Island Resort, explains why:

Beach sand is very nutritious from a plant's perspective, holding everything except nitrogen - an essential element for growth. The sand mass itself is 98% silica with other traces of minerals such as Illmneite, Zircon, Feldspar & Rutile. This virgin sand is mostly yellow in colour and is very water repellant. The yellow colour is a coating of minerals and nutrients surrounding the white quartz core. Sand will also hold more than 33% of its own weight in water as a 'water table'.

From this supply of virgin sand, entire communities of vegetation can develop and they can be recognised by the plants on the surface. These communities have developed to their present state due to availability of fresh water & the age of the dune (which dictates nutrition and access to nutrition). They will continue to change in a dynamic fashion, even during a human lifetime.

In many of the dune systems, microscopic mychorrizal fungus is underground, surrounding the roots of the plants. Because it is underground it cannot use chlorophyl like terrestrial plants to manufacture sugars from the sunlight so instead it takes them from the roots. In return, the fungus strips the outer yellow coating off the sand grains, making the nutrients available for the plant. This symbiotic relationship occurs in many soil & vegetation communities and explains why sometimes plants can be difficult to relocate, if they are specific and/reliant on a particular fungus.

The fungus also changes the colour of the sand, stripping off the yellow coating revealing the white grains underneath. The dune then starts to develop a layer of white sand on top of the yellow sand. White sand drains very readily whereas yellow sand is water-repellant. Any tiny compost particles wash through the white sand and start to accumulate at the ‘B’ horizon, the boundary between the yellow and white layers. The older the dune, the larger the volume of organic material, but it also gets deeper and deeper.