Seasonally inundated grasslands of the Mekong

DeltaTran Triet

Vietnam National University – Ho Chi MinhCity

Delta floodplains

Delta floodplain• Hydrology:

– seasonally inundated by Mekong flood water– nutrient-rich

• Geomorphologic setting:– flat, low-laying, extensive depression areas on both

sides and in between the Mekong and the Bassacchannel

– acid sulphate soils• Vegetation:

– Swamp forest dominated by Melaleuca cajuputi, intermingled with herbaceous marshes

– Permanently inundated marshes/pools– Floating vegetation

U-Minh Thuong

Sea water rise and recede Fresh water arrives

Geology Formation

Sediment >12,000 yBP(old sediment)

Sea water level

Sea water level rise

Marine sediment deposited and shell

appeared

Soil formation (> 6,000yBP)

12,000-6,000 yBP

Sediment contain pyritic materials in 6,000-4,000yBP

Marine sediment deposited in 12,000 - 6,000 yBP

Sediment > 12,000 yBP(old sediment)

Sea water came out

Eroded sediment from up-stream of the Mekong river (rich Fe3+)

deposited in mixed fresh and saline water (rich SO4=) in unaerobiccondition to form Pyrite (FeS2)

Soil formation (6,000 – 4,000yBP)

Fresh water come in

Fe3+ SO4=

Reduction

Fe2+ S-

FeS2

Sediment > 12,000 yBP (old sediment)

Fresh water sediment deposited on top to form the delta and build

river levees

Soil formation (<3,000yBP to date)

Marine sediment deposited in 12,000 - 6,000yBP

Sediment contain pyritic materials in 6,000-4,000yBP

Water level in the dry season

Flood plain wetlands

yriticyritic materialsmaterialsexposed to the airexposed to the air

educe xidi eair/bacteriaflooding/bacteria

Fe(II)(TOXIC)Sulfide

Fe(III)-red hydroxideSulphateH+ (ACIDITY)Jarosite KFe3(SO4)2(OH)6

Aluminium (solid)acid (pH<4)

Al3+(aq.)(TOXIC)

yrite e 2

Potentially ASS

Severely & moderately

ASS

A: Horizon with Organic matters

Bg: Horizon (with Brown/Red mottles)

Bj: Horizon (with Brown and/or Jarosite mottles)

C: Horizon (with Pyritic materials)

A typical profile of Acid Sulphate Soil

Ground water level during the dry season

Melaleuca swamp forest

Seasonally inundated grassland

Eleocharis dulcis

Inundation duration: longInundation depth: medium to highAcidity: highSalinity: low to medium

Eleocharis spiralis

Inundation duration: mediumInundation depth: medium Acidity: highSalinity: medium to high

Lepironia grassland

Inundation duration: mediumInundation depth: mediumAcidity: mediumSalinity: low to medium

Ischaemum grassland

Inundation duration: short to mediumInundation depth: low to mediumAcidity: low to mediumSalinity: low

Panicum grassland

Inundation duration: short to longInundation depth: low to mediumAcidity: low to highSalinity: low to medium

Phragmites grassland

Inundation duration: mediumInundation depth: medium Acidity: mediumSalinity: low

Aquatic vegetation in permanently inundated wetlands

Bassac Marsh

Boeung Prek Lapouv

Tram Chim

Ha Tien Plain

Lang Sen

Threats

• Changing of floodplain hydrology due to:– irrigation– flood control

• Wetland loss due to agricultural expansion

• Pollution

Tram Chim National Park• 7,600 ha• Mosaic of Melaleuca

forests, grasslands and swamps

• Critical habitats for many species of water birds, including the Eastern Saruscrane (Grus antigonesharpii)

Eastern Sarus crane

A flagship species of Tram Chim National Park

Sarus Crane Movements

= KNOWN DRY SEASON LOCATIONS

Mekong Delta

?

Stung Treng, Cambodia

NEST

ADULT

Tram Chim, Vietnam

Eleocharis spp. (Cyperaceae)

tubers

= Water Gate

Hydrological restoration

Water management

0

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5001-

Jun-

95

1-Au

g-95

1-O

ct-9

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1-Fe

b-96

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pr-9

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1-Fe

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Wat

er le

vel (

cm A

MSL

)

Water level

Ground level

Water level inside the core zone of Tram Chim National Park

December, 1992 March, 1994

September, 1996 February, 1998

March, 2001

Water birds increased

Cranes decreased

469

6148 898216734

68

497

365

1052

814741

665

159113

302271

631

503

511

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Hig

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num

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f cra

nes

obse

rved

Number of cranes visiting Tram Chim 1986 - 2006

Number of cranes coming to Tram Chim

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2001 2002 2003 2004 2005 2006

Num

ber o

f cra

nes

Mekong Delta Ang Trapeang Thmor Small Wetlands of Open Forest

CRANE POPULATION IN THE LOWER MEKONG BASIN 2001 - 200