Seasonally inundated grasslands of the Mekong Delta Tran Triet - - PowerPoint PPT Presentation

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Dec 10, 2022 46 likes •487 views

Seasonally inundated grasslands of the Mekong Delta Tran Triet Vietnam National University Ho Chi Minh City floodplains Delta Delta floodplain Hydrology: seasonally inundated by Mekong flood water nutrient-rich

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Seasonally inundated grasslands of the Mekong Delta

Tran Triet Vietnam National University – Ho Chi Minh City

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Delta floodplains

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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 Bassac channel – acid sulphate soils

Vegetation:

– Swamp forest dominated by Melaleuca cajuputi, intermingled with herbaceous marshes – Permanently inundated marshes/pools – Floating vegetation

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U-Minh Thuong

Sea water rise and recede Fresh water arrives

Geology Formation

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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

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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

Eroded sediment from up-stream of the Mekong river (rich Fe3+) deposited in mixed fresh and saline water (rich SO4=) in unaerobic condition to form Pyrite (FeS2)

Soil formation (6,000 – 4,000yBP)

Fresh water come in

Fe3+ SO4

Reduction

Fe2+ S-

FeS2

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Sediment > 12,000 yBP (old sediment)

Fresh water sediment deposited

n 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

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฀yritic ฀yritic materials฀ materials฀ exposed฀to฀the฀air exposed฀to฀the฀air

฀educe ฀xidi฀e

air/bacteria flooding/bacteria Fe(II)(TOXIC) Sulfide Fe(III)-red hydroxide Sulphate H+ (ACIDITY) Jarosite KFe3(SO4)2(OH)6 Aluminium (solid) acid (pH<4) Al3+(aq.)(TOXIC) ฀yrite฀฀e฀2 Potentially ASS Severely & moderately ASS

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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

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Melaleuca swamp forest

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Seasonally inundated grassland

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Eleocharis dulcis

Inundation duration: long Inundation depth: medium to high Acidity: high Salinity: low to medium

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Eleocharis spiralis

Inundation duration: medium Inundation depth: medium Acidity: high Salinity: medium to high

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Lepironia grassland

Inundation duration: medium Inundation depth: medium Acidity: medium Salinity: low to medium

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Ischaemum grassland

Inundation duration: short to medium Inundation depth: low to medium Acidity: low to medium Salinity: low

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Panicum grassland

Inundation duration: short to long Inundation depth: low to medium Acidity: low to high Salinity: low to medium

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Phragmites grassland

Inundation duration: medium Inundation depth: medium Acidity: medium Salinity: low

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Aquatic vegetation in permanently inundated wetlands

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Bassac Marsh Boeung Prek Lapouv Tram Chim Ha Tien Plain Lang Sen

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Threats

Changing of

floodplain hydrology due to:

– irrigation – flood control

Wetland loss due to

agricultural expansion

Pollution

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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 Sarus crane (Grus antigone sharpii)

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Eastern Sarus crane

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A flagship species of Tram Chim National Park

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Sarus Crane Movements

= KNOWN DRY SEASON LOCATIONS

Mekong Delta ?

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Stung Treng, Cambodia NEST ADULT Tram Chim, Vietnam

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Eleocharis spp. (Cyperaceae)

tubers

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= Water Gate

Hydrological restoration

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Water management

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50 100 150 200 250 300 350 400 450 500

1-Jun-95 1-Aug-95 1-Oct-95 1-Dec-95 1-Feb-96 1-Apr-96 1-Jun-96 1-Aug-96 1-Oct-96 1-Dec-96 1-Feb-97 1-Apr-97 1-Jun-97 1-Aug-97 1-Oct-97 1-Dec-97 1-Feb-98 1-Apr-98 1-Jun-98 1-Aug-98 1-Oct-98 1-Dec-98 1-Feb-99 1-Apr-99 1-Jun-99 1-Aug-99 1-Oct-99 1-Dec-99 1-Feb-00 1-Apr-00 1-Jun-00 1-Aug-00 1-Oct-00 1-Dec-00 1-Feb-01 1-Apr-01 1-Jun-01 1-Aug-01

Water level (cm AMSL)

Water level Ground level

Water level inside the core zone of Tram Chim National Park

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December, 1992 March, 1994 September, 1996 February, 1998

March, 2001

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Water birds increased

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Cranes decreased

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469 61 48 89 82 167 34 68 497 365 1052 814 741 665 159 113 302 271 631 503 511 200 400 600 800 1000 1200 1 9 8 6 1 9 8 8 1 9 9 1 9 9 2 1 9 9 4 1 9 9 6 1 9 9 8 2 2 2 2 4 2 6 Highest number of cranes observed

Number of cranes visiting Tram Chim 1986 - 2006

Number of cranes coming to Tram Chim

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200 400 600 800 1000 2001 2002 2003 2004 2005 2006 Number of cranes Mekong Delta Ang Trapeang Thmor Small Wetlands of Open Forest

CRANE POPULATION IN THE LOWER MEKONG BASIN 2001 - 200