Ecological expert Nguyễn Hữu Thiện. — Photo nongnghiep.vn

Ecological expert Nguyễn Hữu Thiện speaks to Nông Nghiệp Việt Nam (Việt Nam’s Agriculture) newspaper on the need for clearer environmental regulations for thermopower plants in the Mekong Delta to reduce risks to the region’s aquatic resources

What are the notable characteristics of the Mekong Delta's fish resources?

The area we need to focus on the most is where the Mekong River tributaries meet the sea, including the river basin and the coastal waters, as these areas are rich in diversity.

Anadromous species, those that live most of their lives in the sea but migrate into freshwater areas to spawn; catadromous are the opposite, meaning they live in freshwater but spawn in the sea; potamodromous species are those living entirely in freshwater but have to migrate long distances through river networks to spawn or hunt.

Take pangasius krempfi (cá bông lau) for example, it’s a freshwater fish but it migrates to the sea in certain phrases of its life. After spawning in the waterfalls of the mid-stream Mekong, the eggs will go along with the water downstream and the baby fish live in the sea until they reach a certain size, then they will swim up the Mekong River to get to southern Laos in May or June to spawn. This is one of the fish species with the longest migration distance in Mekong River. The species is a major catch for communities living on the Tiền and Hậu rivers of the Mekong Delta.

What are the consequences of coal-fired thermal power plants in the Mekong Delta?

The first impact is to the water environment. As thermal power plants draw water from the Hậu and Tiền rivers for cooling, the discharged water – which is usually about 7 degrees Celsius hotter than the ambient water, causes thermal pollution and degradation of water quality.

This leads to a thermal shock for the species as most of them live comfortably only within a narrow temperature range, and if the ambient temperature rises or decreases to a level beyond their tolerance they could weaken and die.

According to the Revised Power Development Master Plan for 2011-20 with a vision to 2030, 12 coal-fired power plants with a total capacity of 15,780MW are planned for the Mekong Delta region. Has your research looked into the thermal pollution level if these plants are built?

According to our calculations, if the input water’s temperature is about 25-27 Celsius degrees (or up to 32 Celsius degrees in the summer), and the discharged cooling water is about 7 degrees higher, then several sections of the Mekong River will suffer from thermal pollution.

If all the plants are built, the total volume of discharged cooling water from them would reach 21.8 billion cu.m per year in 2020-50.

Against the total volume of water that the Mekong River discharges into the sea at about 475 billion cu.m a year, the cooling water volume would be equal to 4.5 per cent, quite a significant amount.

These are our calculations in a normal weather setting, in abnormal cases such as heavy drought in 2016, the impact of cooling water discharge would be even greater. With that said, as these figures are derived from many hypothetical assumptions, they should be for reference only.

Thermal pollution will surely happen, but the extent of the phenomenon remains hard to say to sure. Tides could also impact the heat transfer process, making for inconsistent thermal pollution across the length of the stream. We also expect that the temperature increase might be lower than our projections but the river’s water might retain heat for longer due to alluvium content.

In addition, coal-fired thermal power plants also emit polluting gases like sulfur oxides (SOx) and nitrogen oxide (NOx), which could cause acid rain, which would ultimately pollute the land and water and ecological system of a wider region than where the plants are situated.

Do all the planned thermal power plants need environmental impact assessments approved by agencies?

Usually, a project’s impact is assessed only in a limited geographical region surrounding the project. So when it comes to a cluster of plants along a river, the separate assessment approach would not give a comprehensive judgement of the combined impacts of all the plants on said river.

The interdependent relations between habitats – for example, species that move between the sea and the river water regions in different stages of their lives – should also be taken into account. Impacts from the coal-fired thermal power plants in one place could result in knock-on impacts in a wider region, even beyond our borders.

What are your recommendations?

I have five recommendations.

First, for agencies to make the right decision regarding power development plans, a strategic environmental assessment should be done for the Mekong Delta region. There has already been one assessment like that for the National Power Development Plan VII but the scope of it is the entire country, so there should be one focusing on the particulars of the Mekong Delta.

Second, thermal pollution should be an issue that needs much more attention as aquatic resources in the Mekong River are an important pillar of the region’s ecology, economy, culture and livelihood.

Third, strategic environmental assessments for a project must be conducted before the approval in principle for said project is given, and combined impacts of all projects in the region must also be looked at.

Fourth, the consideration of costs and benefits of power plans cannot only be based on investment and financial rewards but also the ecological and social costs that are fully and appropriately calculated.

Finally, the use of more modern technologies in coal-fired power plants – namely, supercritical (SC) and ultra-supercritical (USC), which are supposed to generate less ash and slag or dust – is important but regulators must set out a limit on emissions or water temperature increases, especially in areas like river mouths. I cannot stress enough the importance of these areas. — VNS