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Quality not quantity greatest threat to key groundwater source

30 August 2016

The greatest threat to sustainable groundwater in the Indo-Gangetic Basin is contamination and not depletion, according to a study co-authored by UCL researchers and published this week in Nature Geoscience.

groundwater

Using groundwater measurements from across the region, the study reveals that over 60% of accessible groundwater is no longer safe to drink or usable for irrigation due to high concentrations of arsenic or salinity.

The Indo-Gangetic Basin is the drainage area of the Indus, Brahmaputra and Ganges Rivers whose underlying  sediments form the world’s most intensively developed groundwater system. This basin alone accounts for a quarter of all groundwater withdrawn globally and supports the livelihoods and agricultural activities of more than 750 million people in Pakistan, India, Nepal and Bangladesh.

Most of the groundwater is used to irrigate food crops, such as rice and sugar cane, but it is also used for drinking water – especially for the cities of Delhi, Dhaka and Lahore.

The study looked at thousands of groundwater field measurements in combination with existing groundwater datasets to reveal a diverse picture of groundwater changes across the Indo-Gangetic Basin over the past decade.

The authors found that groundwater levels are falling in 30% of the basin, particularly near major cities, but are stable or even increasing across the other 70% due to recharge from leaky irrigation canals. However, they also found that for groundwater up to a depth of 200 metres — which represents a volume 20 times greater than the combined annual flow of the Indus, Brahmaputra and Ganges rivers — more than 60% is contaminated by arsenic or salinity.

Co-author, Professor Richard Taylor (UCL Geography), said: “For several years, satellite measurements have found that over the last decade or so groundwater levels are generally declining across this region as groundwater abstraction for agriculture increases.

“However, this study not only places short-term satellite measurements in a longer term context but also examines in much closer detail how groundwater quality and quantity varies. The study found that recent groundwater depletion in some areas actually follows a century-long period of groundwater accumulation. Critically, we also found that the greatest threat to groundwater in the region is water quality, not depletion.”

First author, Professor Alan MacDonald (British Geological Survey), added: “This study highlights the importance of monitoring groundwater quality as well as quantity. These detailed measurements reveal how groundwater levels can be rising as well as falling in the area and also the scale of the problems posed by poor water quality.”

The study was funded by the Department for International Development (DFID) and led by the British Geological Survey in collaboration with an international team of researchers from Pakistan, India, Nepal, Bangladesh, the USA and the UK.

The UCL co-authors of the study are Professor Richard Taylor (UCL Geography), Dr William Burgess (UCL Earth Sciences) and Dr Mohammad Shamsudduha (UCL Institute for Risk & Disaster Reduction).

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  • Dry-season rice crop irrigated with groundwater in Barind, NW Bangladesh (Credit: Dr William Burgess)