Last updated January 31, 2018 at 5:01 pm
Groundwater is being pumped out at rates much faster than can be replenished, and could be a significant contributor of carbon dioxide emissions according to new research.
Groundwater sampling in the Murray-Darling Basin. Image: CSIRO Publishing
Previous studies have looked at the contribution to carbon emissions of pumping groundwater for use in agriculture, in terms of the energy needed to run the electric or diesel pumps to get it out of the aquifer and deliver it to crops.
But this study looked at carbon dioxide emissions that are released from the water itself. Rain contains the same amount of carbon dioxide as the atmosphere, but once it soaks into the ground, it absorbs more carbon dioxide from the soil. Soil carbon dioxide levels are up to 100 times higher than the air because the microbes that live there break down complex carbons and release carbon dioxide as waste, much as we do.
Undisturbed, groundwater can take hundreds to thousands of years to reach the surface again. But humans are pumping out groundwater at an astonishing rate. Around 150 km3 of groundwater are used annually globally. That’s equivalent to 250 Sydney Harbours pumped out of aquifers around the world. The authors estimate that this contributes between 8 and 17 million metric tonnes per year of CO2 to the atmosphere.
This would put groundwater depletion on the top 20 list of sources for carbon emissions according to the US Environmental Protection Agency (EPA) and the Intergovernmental Panel on Climate Change (IPCC).
Currently emissions from release of dissolved CO2 in groundwater are not taken into account in Australia’s carbon budgeting. Australia is dependent on groundwater for agriculture, mining, manufacturing and as a drinking water supply for regional areas. Approximately one third water used in Australia per year, roughly 5,000 GL is said to be sourced from groundwater, but many researchers in the sector consider that actual use may be double this.
“We were somewhat surprised that this hasn’t been accounted for in the literature and in the [EPA and IPCC] evaluations,” said David Hyndman, a hydrogeologist at Michigan State University in East Lansing, Michigan and co-author of the study.
“It’s not going to change the way we think about global climate change. It’s just another factor involved that we need to consider,” said Warren Wood, a hydrogeologist at Michigan State University and co-author of the new study.
Read the original research here.
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