Salt and Arsenic Contamination Ganga basin

According to a new study published by Nature Geoscience, the gravest threat to groundwater in India isn’t over-exploitation but arsenic and salt contamination.
Important Highlights:

• This reports says that 70 per cent of the water table in most of the Indo-Gangetic aquifer — among the largest in the world — is ‘stable and mostly improving’.
• Nearly 23 per cent of the 300 BCM (billion cubic metre) is extremely saline and about 40 per cent contaminated by arsenic
• There is alarming groundwater depletion in northwest India and Pakistan based on satellite imagery from the Gravity Recovery and Satellite Experiment (GRACE).
• Canals built in the 19 and 20 centuries significantly influenced groundwater trends as water accumulated at the origins of the canal tended to “leak out”, leading to high recharge and sometimes floods.
• Groundwater trends were highly variable across India and could change year on year.
• Sixty per cent of the groundwater in a river basin supporting more than 750 million people in Pakistan, India, Nepal and Bangladesh is not drinkable or usable for irrigation.
• The biggest threat to groundwater in the Indo-Gangetic Basin, named after the Indus and Ganges rivers, is not depletion but contamination
• Up to a depth of 200m (650ft), some 23% of the groundwater stored in the basin is too salty, and about 37% “is affected by arsenic at toxic concentrations”
• The Indo-Gangetic basin accounts for about a quarter of the global extraction of groundwater – freshwater which is stored underground in crevices and spaces in soil or rock, fed by rivers and rainfall.
• Fifteen to twenty million wells extract water from the basin every year amid growing concerns about depletion.
• The new study – based on local records of groundwater levels and quality from 2000 to 2012 – found that the water table was in fact stable or rising across about 70% of the aquifer.
• It was found to be falling in the other 30%, mainly near highly populated areas.
• Groundwater can become salty through natural and manmade causes, including inefficient armland irrigation and poor drainage.
• According to a review of India’s water resources by the government in December 2015, India has a usable resource of 1,123 BCM/year of which surface water and groundwater is 690 BCM/year and 433 BCM/year respectively. Setting aside 35 BCM for natural discharge, the net annual ground water availability for the entire country is 398 BCM.

Impact of Arsenic Contamination

• Long-term exposure to arsenic in drinking water can cause cancer in the skin, lungs, bladder and kidney. It can also cause other skin changes such as thickening and pigmentation
• Soluble inorganic arsenic can have immediate toxic effects. Ingestion of large amounts can lead to gastrointestinal symptoms such as severe vomiting, disturbances of the blood and circulation, damage to the nervous system, and eventually death.
• Long-term exposure to inorganic arsenic in drinking water in Taiwan has caused blackfoot disease, in which the blood vessels in the lower limbs are severely damaged, resulting eventually in progressive gangrene.

Impact of Stalinization

• Detrimental effects on plant growth and yield
• Damage to infrastructure (roads, bricks, corrosion of pipes and cables)
• reduction of water quality for users, sedimentation problems
• soil erosion ultimately, when crops are too strongly affected by the amounts of salts

By: Vishal