Lead author Dr. Grant Ferguson argues that there has been an important push in hydrological research over the past few decades to recognize groundwater and surface water as a single resource. But a new study by Ferguson suggests that groundwater is not the same.
Article published in Communications Earth & Environmenthas shown that while groundwater is never completely separated from surface water, there are depths at which groundwater is only loosely connected to the rest of the hydrological cycle.
Ferguson says that in some models, researchers are somewhat arbitrarily setting the level at which groundwater no longer interacts with surface water. This study attempts to give a more accurate figure of how deep this might be.
“It could be centuries or millennia before some of the waters rise and seep into some river,” Ferguson said.
Co-author Dr. Jeffrey McDonnell, professor at the US School of Environment and Sustainability, says this study could help change the water cycle diagrams we all learn in school.
“Instead of a rhythmic flow of water going in and out of the ground, these updated charts will include results from this and other work showing how much water is stuck underground and truly cut off from the global water cycle,” McDonnell said. “This is very different from how the cycle is currently portrayed, where everything that hits the ground ends up returning to the rivers and oceans.”
It has been estimated that there are 44 million cubic kilometers of groundwater on the planet, and previous studies have shown that 2/3 of this is over 12,000 years old. In comparison, some surface waters are less than three months old.
“The mystery of why underground water is so old and river water so young is partly explained by these new discoveries,” McDonnell said.
The real findings of the study cannot be overlooked either, as both Ferguson and McDonnell note that the study could change our understanding of groundwater pollution and its relationship to surface water.
The scientists noted that it is important to establish whether groundwater is sealed off or not, because if humanity wants to store nuclear waste in the ground, sequester CO2, or produce both traditional and new energy sources, we need to know how these systems are interconnected and with the rest of the hydrological cycle.
Source: Grant Ferguson et al, Groundwater deeper than 500 m contributes less than 0.1% of global river discharge, Communications Earth & Environment (2023). DOI: 10.1038/s43247-023-00697-6
