How groundwater affects the carbon cycle

– Keshav R Menon

Conceptual illustration showing how groundwater availability influences plant health and carbon-water interactions across Indian ecosystems (Image: Abhishek Chakraborty)

Groundwater depletion has wide-ranging effects on various ecosystems in India. But there is limited information on how the depletion affects the amount of carbon sequestered from the atmosphere and how this sequestered carbon is linked to the water cycle. This is because most studies in this domain have been limited to specific locations.

A recent study led by IISc researchers and collaborators analysed the efficiency of ecosystems in storing carbon throughout the entire geographical area of India. Using a combination of existing datasets, satellite imaging, and statistical fitting, the team first calculated water table depth (WTD) – the vertical distance between the surface and the level below the ground where the soil gets saturated with water – in different regions. They also measured the amount of chemical energy that the plants produced, measured by the Gross and Net Primary Productivity (GPP and NPP respectively), and the amount of water moved by the plants from the soil to the atmosphere, measured by Evapotranspiration (ET).

Conceptual overview linking water table depth with ecosystem carbon-water processes (left), along with spatial trends in carbon uptake for croplands across India (right) (Image: Abhishek Chakraborty)

Using these quantities, they calculated the plants’ Carbon Use Efficiency (CUE) and Water Use Efficiency (WUE). CUE reflects the balance between the carbon uptake and energy used up for respiration. WUE represents the balance between carbon uptake and water loss.

The team found that if the water tables are deeper, the ecosystems’ efficiency and plants’ productivity are lower, and most regions follow this expected trend. However, this does not hold true during the monsoon in wetter regions of the country. Such regions have shallow water tables, and the soil there becomes easily waterlogged from the rain. Owing to the water table being so close to the surface, the water cannot drain quickly, and the plants’ roots are then deprived of oxygen. This pattern also holds for irrigated croplands across the country.

Such insights can help policymakers identify regions with higher environmental degradation due to overexploitation of groundwater, and tailor strategies for sustainable water use in these regions.

The work was carried out as part of the PhD research of Abhishek Chakraborty, supervised by faculty members Muddu Sekhar and Lakshminarayana Rao at IISc. Chakraborty is currently a postdoctoral scholar at the University of California, Merced.

Research team (Photos courtesy: Abhishek Chakraborty)

REFERENCE:

Chakraborty A, Sekhar M, Bhanja SN, Rao L, Linking groundwater variability to ecosystem carbon and water use efficiencies across India, Ecological Informatics (2025).
https://www.sciencedirect.com/science/article/pii/S1574954125004200

LAB WEBSITES:
https://www.plasmalabiisc.com/
https://civil.iisc.ac.in/~muddu/