Opinion: Floodplain wetlands of the Mekong – going, going, gone?

floodplain-cover A pair of sarus cranes, which have declined precipitously in the Mekong floodplain due to habitat loss and disturbance

The swamp forests, reedbeds and flooded grasslands of the Lower Mekong basin form one of the most biologically important regions on the planet. But these ecosystems are vanishing at an alarming pace. A rapid and irreversible change is taking place in the Lower Mekong basin. Floodplain grasslands and freshwater wetlands are being lost – bustling ecosystems that once supported thriving communities of large mammals and birds. These include the spectacular sarus crane; the greater adjutant, one of the world's largest stork species; and the Bengal florican, a chicken-sized bustard known for its parachuting display flight. Today, these are some of the region's most threatened large birds. Meanwhile, deer, wild cattle and big cats have been virtually extirpated across most of the region by a combination of hunting pressure and habitat loss.

Drenched with nutrients from the monsoon flood pulses, the Mekong's floodplains are incredibly fertile. The Mekong's ecosystems form the heart of the Indo-Burma biodiversity hotspot, one of the most biologically important regions on the planet. New species are constantly being discovered: about 200 new species of plants and animals were recorded in 2020. Among the Mekong's most recognisable species are the sarus crane, the masked finfoot (an elusive aquatic bird), the Siamese crocodile and the Mekong giant catfish, as well as the possibly extinct kouprey (a forest-dwelling wild cattle species).

Graphic by The Third Pole

In Thailand, a glimpse of what these places once looked like can be found at Nong Bong Khai lake and the Nam Kham Nature Reserve, where a compact but recently restored area of riverine reedbeds now abounds with migratory birds such as reed warblers and rubythroats.

The wetlands at Nam Kham Nature Reserve in Thailand

Decline of the spectacular sarus crane

Perhaps the most iconic bird species of the Mekong floodplains is the sarus crane. The only resident crane in Southeast Asia, which boasts a unique subspecies, the sarus crane once occurred widely in the region's lowlands, extending north to Yunnan in China, where it is now extinct.

These majestic cranes breed in the dry deciduous forests and associated wetlands along the floodplains of the Mekong and its tributaries during the monsoon. Towards the dry season, they move downstream to settle in the wetlands along Cambodia's Tonle Sap lake, as well as several wetlands on the upper Mekong delta spanning the Cambodia-Vietnam frontier.

Why are floodplain wetlands being lost?

The Mekong flows down from the Qinghai-Tibetan Plateau in China, where it is known as the Lancang. The river and its many tributaries snake nearly 4,000 kilometres across the hills and lowlands of mainland Southeast Asia, nourishing large areas of Laos, Cambodia, Myanmar and Thailand before spilling into the South China Sea in a vast deltaic plain which spans Cambodia and Vietnam.

Much has been written about the impacts of large dams on the Mekong. The construction of mega-dams has already greatly altered the river's hydrology. More than 10 dams have been constructed on the upper Mekong in China's Yunnan province. Meanwhile, the controversial Xayaburi and Don Sahong dams in the Si Phan Don region on the Laos-Cambodia border, as well as planned dams on the Tonle Sap River, are expected to cause further changes.

How to protect the Mekong's floodplains

The Mekong's remaining wetlands and forests are under siege from unsustainable use of natural resources as Southeast Asian countries strive to advance economic development.

What is urgently needed now is for governments, scientists and conservationists to scale up efforts to preserve the remaining floodplain ecosystems, while restoring connectivity between these landscapes wherever possible. Undammed riverine corridors such as the Sekong River in Cambodia are increasingly rare, and need to be secured for biodiversity and the livelihoods of local people.

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