The study at the Swedish University of Agricultural Sciences, SLU, in Umeå has reviewed analysis results from water samples between 1980 and 2020. The samples were taken by the Geological Survey of Sweden, SGU.
The results show a sharply increased content of carbon dioxide and other forms of inorganic carbon throughout the country. Over the past 40 years, concentrations in groundwater have increased by 28 percent.
"This is an important discovery that can help us better understand the climate system", says Marcus Klaus, the natural geographer at SLU who conducted the study.
Forest growth may be the cause
What the increased level of carbon in groundwater is due to is not certain, but three potential explanations are pointed out.
One reason could be that air pollution has decreased, they affect how rocks are broken down, which in turn affects the turnover of inorganic carbon.
Climate change may also be the reason. When we have a warmer climate, the decomposition of humic substances, i.e. decomposed plant and animal parts, that are present in the soil and groundwater, increases and it produces carbon dioxide.
A third reason could be land use, forests are growing faster in Sweden now than 40 years ago – and trees absorb carbon dioxide, which they then release via roots and soil-dwelling organisms into the groundwater.
More research is needed
What the increased levels mean for climate change is not yet certain. Groundwater can become an additional source of carbon dioxide emissions, or continue to store more carbon dioxide.
"More research is needed on this topic, so far we can only speculate about when the carbon will be released back into the atmosphere. But we know that groundwater plays a central role in the carbon cycle and this is often forgotten," says Marcus Klaus.
Listen to Marcus Klaus talk more about how the results of the study can be interpreted.