In the Mekong Delta, there is a push to grow food with salt water

Now, forces far beyond the river’s iconic mouth are changing that balance.

When sea levels rise, salt water reaches further inland. Climate change makes drought and flood patterns less reliable.

Upstream dams have significantly reduced the sediment carried into the Mekong River, removing material that replenishes the land in the delta and helping its coastline offset rising seas. And now El Niño threatens to exacerbate those tensions.

Vietnamese authorities warned this summer that climate phenomena could cause prolonged heat, reduced rainfall, and exacerbate saltwater intrusion, potentially threatening hundreds of thousands of hectares of rice fields in the Mekong Delta.

For Jack O’Connor, a marine ecologist at UN University Institute for Environment and Human Security in Bonn, the delta offers a glimpse into a question increasingly facing coastal communities around the world: What happens when resistance to environmental change is no longer enough, and communities must learn to live with it?

“The timing, strength of the flood, how hot it will be and when it will be is increasingly difficult for farmers to predict,” said Dr. O’Connor in a recent interview. “Because all of this determines when they will plant their crops.”

Sediment-deficient delta

Climate change is only part of the problem.

The Mekong River begins on the Tibetan Plateau and flows through China and most of Southeast Asia before emptying into the sea in southern Vietnam.

Dams built upstream have trapped much of the sediment that once flowed downstream. According to a scientific study published in 2021sediment reaching the delta has plummeted from about 143 million metric tons two decades ago to about 32 million tons.

These losses are important because deltas are not just land at the edge of the water. It continues to be rebuilt on the riverbank.

Usually, explains Dr. O’Connor, sediment coming from upstream settles along the coast and is trapped by wetlands and mangrove forests. The land gradually rises – a natural defense against rising seas.

But when dams interfere with that process, “you have reduced the supply of fresh water and reduced the supply of sediment,” he said. The sediment, he added, “is valuable for keeping shorelines up to speed with sea level rise.”

Salt invasion

The consequences extend far beyond the coastline. When sea levels rise and fresh water decreases during the dry season, salt can penetrate rivers, canals and groundwater, threatening plants far inland.

This year, the Vietnamese authorities again increase action to protect freshwater supplies as salinity moves upstream during the dry season. The government has called for it long term action to deal with saltwater intrusion, land subsidence and erosion across the delta.

However, avoiding the use of salt is not always easy.

Dr. O’Connor have seen how the solution works can lead to controversial choices. For example, authorities monitoring salinity sometimes close floodgates when river water becomes too salty to safely irrigate rice fields. However, farmers may face more pressing problems.

“They’re worried about salt in their crops,” he said, “but they’re even more worried about the fact that if they don’t have water, there’s no harvest.”

Shrimp cocktail with a twist

Some farmers are responding to environmental change not by preventing the introduction of salt water, but by finding ways to use it.

In some parts of the delta, some have started planting rice and raising shrimp alternately on the same land. Rice is cultivated when conditions are fresher; Shrimp that are resistant to brackish water can be kept if salinity increases.

In An Giang Province, rice shrimp cultivation now covers more than 100,000 hectares of land affected by salt water, and more farmers are adopting organic methods that use less chemical fertilizers and pesticides.

This is part of a broader effort to shift agricultural practices towards a more sustainable and climate-resilient approach.

Dr O’Connor and colleagues have studied broader transitions towards organic rice cultivation in the delta to assess its potential benefits. Their findings also reveal the limitations of adaptation made by individual farmers.

Organic dividends

On test plots, organically grown crops showed signs of greater vigor, while plots planted without chemical pesticides supported much greater biodiversity. Researchers examine dragonflies found that they were much more abundant in organic fields. Spiders and other natural predators are also more abundant, potentially helping with pest control, while fish and crabs in rice fields provide food or another source of income for farmers.

However, other expected benefits turned out to be difficult to obtain.

Water moves freely across the delta, connecting one farm to another. An organic farmer can stop using chemical fertilizers and pesticides, but the water that enters his field may have passed through conventional farming.

“In the lab, it looks really good,” says Dr. O’Connor. “In the field, there are challenges like this.”

Collective flow

The lessons learned, he says, go beyond organic farming: “It starts with the individual, but it really requires collective effort and cooperation on a broader scale.”

The larger dilemma is that farmers can change what happens on their own land, but many of the factors that change that land are outside their control: agricultural practices in the surrounding environment, water management decisions by authorities, dams hundreds of miles upstream, and, ultimately, global warming.

The bigger question is where protection ends and adaptation begins.

Sometimes that means changing what has already grown. Sometimes that means accepting the salt water rather than trying to get rid of it.

Mangrove forest management

And sometimes this means restoring ecosystems like mangrove forests, which trap sediment and buffer coastlines but can compete with agriculture for increasingly valuable land.

For Dr. O’Connor, such measures will only be successful if the communities that depend on the landscape have a stake in them. Restoring mangrove forests for climate adaptation, he said, “must be done in a way that is equitable and involves local communities.”

The sea may be moving towards the Mekong Delta. The more difficult question is how much the people who live there might be changed by it.