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

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 • 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

Sea water rise and recede Fresh water arrives Geology Formation U-Minh Thuong

Soil formation (> 6,000yBP) Sea water level Marine sediment Sea deposited and shell water appeared level rise 12,000-6,000 yBP Sediment >12,000 yBP (old sediment)

Soil formation (6,000 – 4,000yBP) Eroded sediment from up-stream of the Mekong river (rich Fe3 + ) Fe 3+ = SO 4 deposited in mixed fresh and saline water (rich SO4 = ) in unaerobic Reduction condition to form Pyrite (FeS 2 ) Fe 2+ S - Sea Fresh water water came come in out FeS 2 Sediment contain pyritic materials in 6,000-4,000yBP Marine sediment deposited in 12,000 - 6,000 yBP Sediment > 12,000 yBP (old sediment)

Soil formation (<3,000yBP to date) Fresh water sediment deposited Flood plain wetlands on top to form the delta and build river levees Water level in the dry season Sediment contain pyritic materials in 6,000-4,000yBP Marine sediment deposited in 12,000 - 6,000yBP Sediment > 12,000 yBP (old sediment)

฀yritic materials฀ materials฀ ฀yritic exposed฀to฀the฀air exposed฀to฀the฀air Severely & Potentially moderately ASS ASS air/bacteria ฀xidi฀e ฀educe flooding/bacteria Fe(III)-red hydroxide Fe(II)(TOXIC) Sulphate Sulfide H + (ACIDITY) ฀yrite฀฀e฀ 2 Jarosite KFe 3 (SO 4 ) 2 (OH) 6 Al 3+ (aq.)(TOXIC) Aluminium (solid) acid (pH<4)

A typical profile of Acid Sulphate Soil A: Horizon with Organic matters Bg: Horizon (with Brown/Red mottles) Bj: Horizon (with Brown and/or Jarosite mottles) Ground water level during the dry season C: Horizon (with Pyritic materials)

Melaleuca swamp forest

Seasonally inundated grassland

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

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

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

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

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

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

Aquatic vegetation in permanently inundated wetlands

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

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 Sarus crane ( Grus antigone sharpii )

Eastern Sarus crane

A flagship species of Tram Chim National Park

Sarus Crane Movements = KNOWN DRY SEASON LOCATIONS ? Mekong Delta

Stung Treng, Cambodia ADULT NEST Tram Chim, Vietnam

Eleocharis spp. (Cyperaceae) tubers

= Water Gate Hydrological restoration

Water management

Water level (cm AMSL) 100 150 200 250 300 350 400 450 500 50 0 1-Jun-95 1-Aug-95 1-Oct-95 Water level inside the core zone of Tram Chim National Park 1-Dec-95 1-Feb-96 1-Apr-96 1-Jun-96 1-Aug-96 1-Oct-96 1-Dec-96 1-Feb-97 Water level 1-Apr-97 1-Jun-97 1-Aug-97 1-Oct-97 1-Dec-97 1-Feb-98 Ground level 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

March, 2001 December, 1992 March, 1994 February, 1998 September, 1996

Water birds increased

Cranes decreased

Number of cranes coming to Tram Chim 1200 Highest number of cranes observed 1052 1000 814 741 800 631 600 665 503 497 469 511 400 365 159 302 200 271 113 89 68 82 167 48 34 61 0 6 8 0 2 4 6 8 0 2 4 6 8 8 9 9 9 9 9 0 0 0 0 9 9 9 9 9 9 9 0 0 0 0 1 1 1 1 1 1 1 2 2 2 2 Number of cranes visiting Tram Chim 1986 - 2006

CRANE POPULATION IN THE LOWER MEKONG BASIN 2001 - 200 1000 Number of cranes 800 600 400 200 0 2001 2002 2003 2004 2005 2006 Mekong Delta Ang Trapeang Thmor Small Wetlands of Open Forest