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Dry land isn’t really dry. It’s saturated with truly vast volumes of groundwater, hidden in the spaces of the earth we walk on. How much? Recent estimatesIt amounts to almost two billion Olympic swimming pools of water stored in continental crust’s upper 10 km.
Groundwater has been hugely useful for us as a source of water for our agriculture and drinking. This extraction will only increase as the earth heats and waterways dry up. But there’s a hidden problem. We used to think the organic matter in groundwater didn’t react when brought up. Unfortunately, the opposite is true. Our Research in progress published in Nature Communications has found when groundwater – especially from deep down – is pumped to the surface, it brings with it dissolved organic matter preserved from long ago. This matter can easily become carbon dioxide once it has been exposed to sunlight and oxygen.
Groundwater is likely to be another source of planet-heating greenhouse gasses, one that is not included in our carbon budgets. How large? We estimate up to the same amount of dissolved organic carbon as that pumped out by the Congo River each year, the world’s second largest by volume.
This problem will only get worse as we over-extract groundwater, forcing us to search for deeper water that contains more of this greenhouse gas-producing organic material. This unexpected source of greenhouse gas must be included in carbon budgets.
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So how can groundwater become a source for greenhouse gas?
Groundwater can remain underground for millions of years, with its chemical composition based on the rocks or earth it’s surrounded by. The dissolved organic material is very slow to degrade during this time. That’s because it’s dark down there and there’s no way of replenishing oxygen that would usually be dissolved into the water from the atmosphere.
Continue reading:
Groundwater: We must protect the groundwater reserves around the globe
Groundwater enters the air and daylight through our bores, pumps, and other means. Natural flows account for more than half of all groundwater flow at the moment. Every day, groundwater seeps out of the world’s coastlines at a rate of 13 times the water in Sydney Harbour. By contrast, all the world’s bores pump up around five Sydney Harbours a day. (The Australian unit is the measure of water. Sydharb500 gigalitres.
We have analyzed the oldest dissolved organic matter from deep groundwater to determine what happens to it. This organic matter had been in the groundwater more than 25,000 year.
Our research showed that molecules retained in dark, oxygen-depleted deep-groundwater environments for long periods of time were more stable than those which are usually broken down by sunlight and greenhouse gas-producing microbes.
Groundwater is made up of dissolved organic matter. It contains carbon, oxygen, and hydrogen-containing molecules. Some of these molecules can easily be broken down by microorganisms. Others can be transformed into new molecules or carbon dioxide through sunlight.
Use global estimatesWe calculated the amount of groundwater dissolved material and determined how much was brought up to the surface via bores or pumped out to sea. Each year, that’s around 12.8 million tonnes.
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What does this mean to our carbon budget?
We now know that groundwater is a source of carbon, so we need to consider it when we address climate change. To accurately predict future climate changes and the speed at which we must move, we need information about all carbon sources and removal routes.
Continue reading:
Ancient groundwater: Why your water may be thousands years old
Global carbon budget estimates currently ignore groundwater as a source of carbon. This needs to change, particularly as we know that groundwater is likely to be used in ever greater volumes as climate change causes waterways and lakes to dry out.
This is even more pressing, given Australia’s population is Expected to hitIn the next 40 years, there will be nearly 40 million. This growing population requires more groundwater for agriculture, industrial and domestic use.
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Despite the vast volumes of groundwater in the earth’s crust, most of it is very hard to extract. Many artesian wells are being tapped at the surface. In many places, there is an over-extraction problem. Wells are already being drilled. running drySome areas are agricultural.
When the easy water runs dry, we might have to get boring. extract deeper, older water. These ancient waters contain more organic molecules, which can be converted into carbon dioxide if we bring them up. This suggests that groundwater is a potential carbon source and must be included in carbon budgets.
