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Water balance of peatland hydrological unit (PHU)

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Presented by Azwar Ma’as, Professor at the Faculty of Agriculture, Gadjah Mada University, at "Online Workshop Series:Exploring Criteria and Indicators for Tropical Peatland Restoration", on 2 Sep 2020.

In this session Prof. Ma’as shared insights from hydrology and water balance standpoint. These biophysical factors are important for the development of criteria and indicators for peatland restoration, particularly ensuring appropriate consideration for the water balance of each PHU.

Publié dans : Environnement
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Water balance of peatland hydrological unit (PHU)

  1. 1. Water Balance of Peatland Hydrological Unit Azwar Maas Senior Lecturer in Soil Science Department, Faculty of Agriculture. Gadjah Mada University. Yogyakarta
  2. 2. The natural condition of Tropical peatland and disturbed by Human Activities • Closed nutrient cycles • Varies vegetation/flora growth and production adapted to wet, thicker by time to form Dome • Varies fauna growth and developed • Always wet, shallow ground water through water balance (hydrophilic) • Human live ajusted to the natural resources • Converted Peatland to monoculture dryland tree vegetations • Lost of peat formation • Oxidation, speed up decomposition by releasing carbon dioxide and DOC • Subsidence • Bare peat surface, even GWL <0.4m the peat surface can become hydrophobic --> potential burning Important: Utilization of peatland creates negative impact to the environment sooner or later
  3. 3. Water Balance in Nature of Peatland Hydrological Unit (PHU) • Eroded soil mineral particles from upstream rivers, • sedimented to the swamp until shalow enough for the aquatic plants to grow • The trees adapted to wet condition for growth • Infilling woody remnant to shallow baseline mineral sedimentation in swampland • Topogeneous peatland is formed • Inflow from rain, river, sea tidal, upland border • Outflow to river, sea, and evapotranspiration, interception plant canopy • Ombrogeneous peatland is formed above Topogeneous peatland • Inflow: rain • Outflow: to the river, sea, evapotranspiration, Interception plant canopy Picture Source: Noor, 2001, quoted van de Meene, 1984). Important: More attention to Water Balance in Ombrogeneous type of PHU
  4. 4. Water Management (Water Balance) in the Peat Hydrological Unit (PHU/KHG) • Tertiary Drain Canal does not touch the secondary channel above it Ideal Sharing water KHG/Sub-KHG Border drainage of sub KHG (Outflow) An example water management KHG Batanghari Air Hitam Laut, Jambi. Individual concession, independent à no sharing water Remark: Sharing water in existing water management individual concesion, difficult to adjust the ideal water sharing
  5. 5. Case Study : Tebing Tinggi Peatland • Tebing Tinggi area is an island peatland, Surrounding by sea, The only source of frest water is rain • PP 71/2014: At least 30% of KHG in dome and surounded area being conservation areas with peat thickness 6m up to 12 m • 30% x 138.000 ha = sekitar 42.000 ha, BD 0.1ton/m3 • Potential water storage in the peat thickness (assume as landscape) in average of 2.5 m being used for conservation: 42.000.x100x100x2.5x0.9 ton of water = 904 milion ton of water. • This potential water with subsurface slow moving water able to keep the surface peatland still in hydrophillic status at least if no rain 2 months consequtively if still in natural forest and good eco-hydro system. The utilization function should have good canal blocking. Source: Besri Nasrul Dissertation 2019
  6. 6. Concluding remarks • Semi-detailed peat depth mapping and detailed topography for each PHU are main parameters to divide at least 30% of conservation/protected zone and utilization zone, especially for Ombrogeneous PHU • The existing condition, water sharing among stakeholders in one PHU or sub-PHU dificult to implement. Non-technical aspect also factor to be considered for future restoration action • Restoration planning for rewetting of PHU by sharing water with water balance concept. Stakeholders in both government and consession, local settlers must be involved in planning up to implementation, especially for those who are not used to the concept of sharing water
  7. 7. THANK YOU