High salinity concentration in northern districts’ groundwater

Salinity is increasing in ground water in the northern districts of Bangladesh, finds a recent study conducted by the Bangladesh Water Development Board (BWDB).

The scientists of this government organisation found the rising level of salinity in the underground water in areas where salt is being used for fish farming.

Intensified salinity in coastal areas has already turned into a critical issue for Bangladesh. In this situation, water, soil and the environment experts dubbed this finding of high concentration of salinity in the northern districts’ ground water far away from the coastal areas as “surprising” and “dangerous”. They think this salinity could widely affect the lives of the people of the areas including their potable water supply and agriculture.

Bangladesh observed the World Water Day on 22 March in such a context. The theme of the day this year is “Leveraging Water for Peace”.

The Ground Water Hydrology department of BWDB regularly collects water samples from around 1,000 areas. The department found a sudden rise in salinity concentration in the groundwater samples collected from the northern districts nearly six months ago.

The department’s director Anwar Zahid found this. He said, “I studied the groundwater by another machine as I was a bit suspicious about the finding. There too I got the same results. There was a fish farming pond nearby the spot from where the sample was collected. The owner of the pond informed me that he uses salt especially during the winter to protect the fish from a certain kind of disease. Then I thought we need to conduct a large-scale study on the matter.”

The Ground Water Hydrology department then conducted a study in Puthia, Bagmara and Durgapur of Rajshahi, Atrai of Naogaon and Singra and Naldanga of Natore.

The study was conducted on water samples collected from 100-feet depth of the ground near 49 ponds in six upazilas. Measuring the electrical conductivity (EC) is the general method of ascertaining the salinity concentration in soil, with the EC reading increases if the salinity is high.

As per the Bangladesh standard, if the EC remains within 2,000 microsiemens per centimetre water, it is potable, while the range for irrigation water is 3,000 microsiemens. Though no samples collected from the areas near 49 ponds crossed the 2,000 microsiemens ceiling, those were found to be doubled or tripled from their previous reading of 200-300 microsiemens.

The highest salinity concentration of 1,100 microsiemens was found in samples collected from Atrai in Naogaon, Durgapur in Rajshahi and Singra in Natore.

The study also revealed that the salinity concentration in groundwater is higher in areas where salt is being used for a longer period of time.

In Singra of Natore, the EC reading was found to be between 576-666 in samples collected from areas of ponds where salt use is relatively low and the reading was between 806-1100 in samples collected from areas of ponds where salt use is high.

Study team member Shahadat Ali remarked that the spreading of salinity depends on the thickness of and density of the surface. He said of the six upazilas, Bagmara is situated in the Barind tract. The thick and dense red clay layer obstructs the spread of salinity. That is why the concentration of salinity was found to be lower in the samples collected from the upazila. The EC reading did not cross 745 in samples collected from areas where salt has been in use for long.

Asaduzzaman from Shimla area in Atrai upazila of Naogaon farms fish in eight upazila. He said farm fishes suffer from a type of sore in November-December every year. He uses nearly 5 kgs salt per bigha at the advice of fishery officials but he was not aware that the groundwater quality is deteriorating for this use of salt.

Mohammad Rafiq from Bagmara also said the same, mentioning that he uses around 5-8 kgs salt per bigha in winters.

Chief scientific officer of Khulna divisional office of Soil Resource Development Institute (SRDI) GM Mostafizur Rahman works on soil salinity. He said, “Salinity could spread through osmosis or through spill over of ponds during the floods.”

This could have serious implications since fish is farmed across the whole country and 57 per cent of the freshwater fish is farmed in 2,519,872 ponds, said the Department of Fisheries.

Speaking about using salt in ponds for fish farming, Department of Fisheries deputy director Alok Kumar Saha said, “We advise to use salt in ponds during winters as a type of fungus attacks fishes that season.”

He, however, questioned the data regarding the rising salinity concentration in groundwater for using salt in fish farming. He said the amount of salt usage is not so high that it could enter the groundwater. Alok stressed that a detailed study is required in this regard.

BWDB’s study team head Anwar Zahid also did not decline the necessity of further research in this regard. “We worked following the scientific method and the result is worrying. There are ponds across the country where salt is being used. That is why further research is required.”

Researchers think the use of salt in ponds could lead to rising level of salinity in groundwater.

Hydrology expert professor Mujibur Rahman of United INternational University dubbed the BWDB’s study findings as “surprising” and “dangerous”.

He told Prothom Alo, “This study has made us aware of a completely new kind of danger appearing in nature. If this trend of salinity rising continues, this could create a crisis in the northern districts where people are facing scarcity of water. This could also affect crop production. Above all, this could affect the lives of people in a negative way.”

* This report was originally published in the print and online editions of Prothom Alo and has been rewritten in English by Shameem Reza