It’s prolific, peculiar, fundamental, and all too often, unappreciated. Dr Charles Merfield marvels over the properties of banged-up stardust and explains why it is essential to life on Earth.
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Water is the weirdest substance there is! Nothing has physical and chemical properties like it. It is totally bizarre even though it is one of the most common chemical compounds on Earth.
It is the only common material that exists as solid, liquid, and gas over the very narrow range of temperatures found on Earth. It is transparent to visible light – most things are not – so aquatic plants can get sunlight to photosynthesize. Water vapour is opaque to infrared light so it’s an important greenhouse gas that is manipulated by Gaia to keep our climate optimal for life.
It’s at its most dense at 4°C when it is still liquid so the solid phase – ice – floats: most solids sink in their liquids. If this was not the case, water bodies from streams to oceans would freeze from the bottom up and kill most living things in them. Floating ice acts as insulation allowing life to thrive underneath it.
Its latent heat of vaporisation is enormous, meaning it takes a lot of energy to turn liquid water into true steam, which is vital for keeping land species cool, avoiding desiccation, and driving weather systems.
It’s also the most effective solvent there is: even gold and quartz dissolve in water at the high temperatures and pressures deep underground. Water is made of two hydrogen atoms and one oxygen. Oxygen is the third most common element on earth, accounting for 21 percent of the atmosphere, and is only created in the thermonuclear furnace of stars. Nearly all the hydrogen in the universe was produced in the Big Bang. That water running through your fingers is thus two-thirds the product of the birth of the universe and one-third stardust! And that is just the start of it. The list of water’s weirdness just goes on and on.
Water dissolves and moves the chemicals of life through plants. It is taken up from the soil by roots along with dissolved inorganic nutrients such as nitrates and phosphates. This was Justus von Liebig’s great discovery – that plants take up nutrients in soluble inorganic forms, not as organic matter.
These mineral nutrients are then transported throughout the plant by the xylem, part of the plant’s vascular system. Xylem is dead – it is the heartwood in trees – so to get water to move through the xylem vessels there are two main mechanisms.
The first is transpiration – the loss of water from leaves through the stomata. This causes the water in the xylem to come under tension, pulling it upwards, just like a hand pump pulls water up from a well. Plants can control transpiration by opening and closing their stomata.
The second is root pressure, which is caused by roots increasing the concentration of mineral ions, causing water to flow into the roots, via osmotic pressure, and then forcing it up the xylem. In some trees, there is enough root pressure to raise the sap five metres above the ground. Combining transpiration and root pressure, water is moved from the soil to the tops of the tallest trees which can be 100m high!
Once carbohydrates and other soluble organic compounds are made by photosynthesis, the phloem then carries those compounds and the energy they contain round the plant, including back down to the roots. Phloem is alive, unlike dead xylem, and uses special conducting cells, called ‘sieve elements’, which actively transport the sap through the phloem.
Just as water is vital to plants, it’s just as vital to soil life. However, while plants can regulate their water content to some extent by changing uptake rates and losses from the stomata in their leaves, soil life just has to make do with what nature provides.
If soil becomes waterlogged and devoid of oxygen only anaerobic organisms can thrive, aerobic ones shut down, or produce survival structures such as spores.
If the soil is too dry, then there is not enough solvent of life to allow biochemical reactions to occur, so all life shuts down.
Living organisms are what convert ground-up rock into soil – the ‘Living Soil’ that organic farming pioneer Lady Eve Balfour promoted.
Life creates structure in soil, it creates soil aggregates: small crumbs of soil. Between these crumbs are holes called pores, which form a massive network of channels allowing water and air to move through the soil. The best comparison is a bath sponge – which is basically a bunch of holes. Healthy soil should be around 50 percent holes and 50 percent solid soil particles, all of which is impossible without water.
Many of the planetary crises humanity face are due to our disruption of global cycles. The problem with fossil fuels is not the energy they release, it is that they severely disrupt the carbon cycle. Likewise, we are meddling with the water cycle at our peril.
A large part of this is due to our meddling with the carbon cycle and the resulting climate heating, but also due to the massive deforestation we have undertaken which reduces the amount of water vapour vented to the atmosphere via transpiration. For example, the Amazon rain forest is a self-perpetuating system – it pumps huge amounts of water vapour into the atmosphere that creates the rain which makes it a rainforest. If humans keep cutting it down it will reach the point where there is not enough rain to support the rainforest and it will switch to the default ecosystem of savannah, which is dry with few trees to release water to the sky. The changes we are making to the world’s land-based ecosystems is now so vast that we are starting to see the negative effects of this on the global water cycle and therefore our climate and weather.
The water and nitrogen cycles are also highly interlinked as it is water draining from soil that carries soluble nitrates from the soil to streams, rivers, and eventually the oceans. Without water draining from the soil, nitrate cannot be leached – regardless of how much nitrate there is in the soil. This is why regional councils are laser-focused on best irrigation practices for farmers – to ensure that irrigation is used in such a way that minimises soil water drainage and so minimises nitrate leaching. The same applies at home: don’t overwater. Give the soil enough water to wet up to 10 to 30cm of topsoil, but no more.
So how important is water? Infinitely! All life, including humans, are water-based life forms. Of the Earth’s surface, 75 percent is covered in water. Indeed, it’s rather strange to call a planet that is mostly covered in water after the minor amount covered in soil. We only need to look to our neighbour, Mars, to see what happens to a planet that is careless enough to lose its water. It has an atmosphere made almost entirely of carbon dioxide, temperatures that range from −110 to 35°C with screaming winds whipping up the surface into immense dust storms. So be very glad Earth has kept hold of her water and next time you get the hose out to water the garden, ponder some of the vital roles water plays in life on Earth.
Dr Charles ‘Merf’ Merfield is an agroecologist who heads the Biological Husbandry Unit Organics Trust Future Farming Centre, consults and advises in sustainable agronomy and is co-owner of Physical Weeding. See merfield.com