Groundwater in the Cuu Long (Mekong) Delta city of Can Tho is heavily polluted by contaminants released by aquaculture farms and industrial activities, according to city officials
The city’s 12,216 aquaculture farms use at least 70 billion litres of clean water per day.
The waste water discharged into the environment by these ponds has elevated the COD (chemical oxygen demand) in the groundwater to 10mg higher than the normal level. One litre of aquaculture waste water contains 80mg of COD.
The COD test is commonly used to measure the amount of organic compounds in water, and most applications of COD determine the amount of organic pollutants, making COD a useful measure of water quality.
Industrial parks and facilities have also contributed to the excess by discharging 45 million litres of waste water per day, with one litre containing 150mg COD.
"Although the Hau River, which runs across the city, has a powerful water current, all COD content can’t be swept out to sea and the proportion of that in groundwater increases day by day," said Ky Quang Vinh, director of the city’s natural resources and environment monitoring and survey centre.
Annual tests from 1998 to 2008 showed that COD content in the Can Tho River had risen dramatically, with one litre containing only 3mg in 1998 but 28mg in 2007. "But it had a slight decrease last year," Vinh said.
The groundwater has also been polluted by suspended solids, iron content, nitrite and ammonia.
"During the dry season, the city can experience a shortage of water for domestic daily use and production, and it could continue if these conditions remain," he said, adding that the temperature was rising in the area by 0.20C each year. The average rainfall had dropped by 200mm per year, and the water current of the Hau River had fallen also, he said.
By 2014, residents may not be able to pump underground water with pipes drilled into the ground, he said. "At that time water shortage could become severe because it only takes 12km for salinated water to reach the city."
Nguyen Van Tu, deputy chairman of the city’s Union of Technology and Science Associations, said aquatic resources in local rivers and canals had fallen by half and the alluvium content had dropped as well.
He said the major impact had been pollution, but hydro-electric dams on the upper Mekong River that had reversed water flow had also contributed to the problem.
"We should stop the use or construction of dyke systems that seriously affect the flow of rivers," Tu said.
Vinh said the Cuu Long Water Resource Protection Association should set up a project to regulate the use of water for hydro-electricity and agricultural irrigation, exploitation of water in aquaculture, and treatment of waste and waste water.
He said it was urgent to establish a network to monitor and survey groundwater in the vast basin in the region.
Le Anh Tuan from Can Tho University’s climate change study institute said any environmental protection and climate change action should follow a five-step solution, involving analysis, awareness, advocacy, action and adaptation.
The so-called 5A cycle would require the involvement of scientists, public authorities, residents and policymakers, among others.