14.3 WETLANDS

Ecological value and key biodiversity 'flagship' species / Human use / Threats / Management dilemmas and conflicts

Key wetlands along the Mekong--
Important wetlands exist throughout the Mekong Basin, including the Mekong River delta, portions of the Mekong River mainstem, and wetlands on tributaries to the Mekong River.

Mekong River Delta. The Mekong River delta begins in Cambodia near Phnom Penh and extends to the sea coast of Viet Nam. The delta is comprised of an elaborate network of river channels, large seasonally inundated plains, rice paddy areas, shrimp and fish ponds, remnants of natural forests and marshes, and tidal mudflats. Important natural components of the estuarine and delta wetlands are the extensive mangrove swamps, tidal mudflats and Melaleuca forests. Protection areas within the delta have been established to protect bird colonies, coastal marshes, Melaleuca forest, mangrove forest, and estuarine wetland.

Mekong River mainstem. After the Mekong River passes through relatively narrow valleys of Myanmar and northern Lao PDR, the river enters lowlands characterized by increasingly wide valleys eventually reaching the broad floodplains of Cambodia before flowing to the Mekong River delta. Wetlands occur at the confluence of tributaries, such as the Nam Ngum and along the floodplain. Downstream from Khone Falls, the river valley is comprised of high natural levees and broad fluviatile lowlands that contain backwater swamps that may remain flooded even during the dry season. Important mainstem wetland areas in Cambodia include Stung Treng in the northeast.

Tributaries to the Mekong River. Important wetlands occur on tributaries to the Mekong River. The largest and best known of these is the extensive floodplain around the Great Lake and Tonle Sap River in Cambodia. The Great Lake is the largest permanent fresh water lake in South East Asia and is surrounded by a large fresh water swamp forest, approximately 20-30 km wide. The lake supports one of the largest freshwater fisheries in the world, with elaborate fisheries established to capture fish when floodwaters recede from the lake and surrounding forest. Large wetlands occur to the north of the Great Lake, on the Stung Sen which flows into the Great Lake at its outlet (the Tonle Sap River) and in Thailand on two major tributaries to the Mekong River, the Mun and Chi rivers. Upper reaches of the Stung Sen contain seasonally flooded marsh and grasslands. Important wetlands on the Chi and Mun rivers include important areas for over wintering waterfowl. Smaller wetlands occur at additional locations along tributaries in Thailand and Lao PDR, including significant overwintering areas for birdlife such as the Chiang Saen Basin and Tha Ton Marsh in northern Thailand.

Ecological value and key biodiversity 'flagship' species--
Mekong River Delta. Although heavily developed for agriculture, the Mekong river delta contains important habitats, with some of these areas possessing notable bird colonies. Wetlands in the delta are important because they often represent the remaining units of ecosystem types within the basin, such as the Melaleuca forests. They also offer remaining habitat for biological groups such as overwintering waterfowl and contain species-at-risk. Bird species at risk in delta wetlands include the endangered Giant Ibis Thaumatibis gigantean, White-shouldered Ibis Pseudibis davisoni, Sarus Crane Grus antigone, and rare White-winged wood duck Cairina scutulata. Other taxonomic groups have species at risk, including reptiles such as the River Terrapin Batager basksa.


Mekong River Main-stem. The Mekong River is comprised of the main channel, which is important perennial habitat for a diverse assemblage of fish species, and floodplains that provide critical seasonal habitat for many species. As the floodplains become inundated during seasonal flooding, most of the river fish populations migrate laterally into those areas for spawning. One fish species, the giant catfish Pangasianodon gigas, migrates several thousand kilometers to and from spawning areas in the main channel, though numbers have been reduced to near extinction in many areas downstream from its spawning area in the Mekong along northern Lao PDR. In northern Thailand there is an important wetland (Chiang Saen Basin) that includes deepwater areas along the river used by giant catfish. Wintering and resident waterfowl that are scarce or absent elsewhere in Thailand also are found in this location.

Three species of dolphin use the main channel (Irrawaddy dolphin Orcaella brevirostris, rare Chinese white dolphin Sotalia chinensis, and Black finless Porpoise Neophocaena phocanoides), though only the Irrawaddy dolphin occurs upstream of Khone Falls. The endangered Siamese crocodile Crocodylus siamensis, rare Smooth-coated Otter Lutra perspicillata and Fishing Cat Felis viverrina are reported to still occur in some areas.

Tributaries to the Mekong River. The large swamp forest around the productive Great Lake in Cambodia supports a large number of endemic fish species and refuge for many bird species, including the endangered Milky stork Mycteria cierea, Giant ibis Thaumatibis gigantean, White-shouldered ibis Pseudibis davisoni and eastern Sarus Crane Grus antigone. Species using the Stung Sen wetland, to the north of the Great Lake, are poorly known but are believed to include the same endangered bird species and, in addition, the endangered White-winged wood duck Cairina scutulata, Siamese crocodile and kouprey Bos sauveli.

In Thailand, wetlands in watershed of the Chi and Mun rivers contain diverse wetland areas along both rivers, these include:

• Chi River watershed;

• A small permanent lake that is fringed with aquatic vegetation and provides daytime refuge for wintering wildfowl, particularly ducks; and

• A large, rich wetland complex that provides wintering habitat for a large number of waterfowl and raptors.

• Mun River watershed;

• Riverine marshes in an area of high human density at the confluence with the Chi River;

• Marshes along the banks of the Mun River; and

• Along a tributary (Lam Nam Mat) to the Mun River, seasonally flooded marshy land, two Non-hunting Areas that protect wildlife in large floodplains and marshes around several reservoirs.

Wetlands on the Lam Nam Mat provide habitat to wintering birds and one is the only location in Thailand known to have Comb ducks (Sarkidiornis melanotos) and has rare White-winged wood ducks (Cairina scutulata).

Near the border with Cambodia, a small permanent river that flows into the Mekong River has a floodplain wetland (Lam Dom Yai) containing the White-winged wood duck and possibly the Siamese crocodile.

In northern areas of Thailand there are important wetlands along the Mae Kok and Mae Ing rivers; these include:

• Nam Mae Kok

• A marsh ecosystem that is used by a large variety of wintering birds; and

• A complex of small pools, reed-beds, grassland and rice paddies that is used by wintering birds but has been poorly studied.

• Nam Mae Ing

• Several wetlands comprised of permanent lakes and ponds that are fringed by marshes and provide habitat for wintering birds; and

• A wetland that is a complex of small pools and another that is an extensive marsh.

In southern Lao PDR near the border with Cambodia, is a large marsh surrounded by seasonally flooded forest (Bung Nong Ngom), which has a rich fish fauna and a number of large mammals (Asian elephant, tiger, clouded leopard, deer, kouprey), resident and migratory waterfowl and the endangered Siamese crocodile. Further to the north, permanent marshes exist at the confluence of several tributaries (Pak Sane and Pak Sa marshes) with the Mekong River. The Nam Ngum reservoir is the largest impoundment in Lao PDR and supports a diverse fish fauna.

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