Mangrove

Background & Scope

Ecosystem Services by Mangroves

Mangroves provide critical ecosystem services (nutrient cycling, pollutant capture, carbon sequestration, fisheries and biodiversity) and can reduce coastal vulnerability by buffering wave energy. Intertidal vegetation has been used for coastal defence in Northwest Europe for more than 15 years under the names of managed realignment or depoldering, though its use holds much promise in Southeast Asia.

Utilising field measurements, remote sensing, flume studies and hydrodynamic modelling (Delft3D), this project quantified the effectiveness of mangroves for wave attenuation, and the critical thresholds that determine their survival in Singapore and Thailand. This will aid their use for sustainable coastal defence in Southeast Asia, and increase the success of future restoration efforts.

Project Components

  • Mangrove colonization processes – We researched early mangrove colonization to determine hydrodynamic and inundation thresholds in the lab and the field. Such information is crucial for mangrove restoration efforts.
  • Hydrodynamic attenuation and sediment dynamics – Field research in Thailand quantified the effectiveness of mangrove structures to reduce incoming hydrodynamic energy, and implications for sediment deposition and medium-term surface accretion
  • Mangrove vulnerability to sea level rise – Mangrove surface elevation must increase at a greater rate than sea level rise or else become vulnerable to ‘ecological drowning’. In collaboration with the US Geological Survey, we were one of the first to install the Surface Elevation Table methodology in SE Asia to measure mm change in mangrove surface elevation, and elucidate soil processes and subsidence. We were also creating digital elevation models of major mangrove sites in Singapore.
  • Remote sensing of mangroves – Research quantified national/regional-scale mangrove dynamics and the drivers of change, with focus on Peninsular Malaysia and Myanmar.
  • Uncertainty in environmental information – We are interested in causes of scientific data uncertainty, policy implications and methods to improve the reliability of baseline information. Such information is crucial to the robust implementation of environmental policies such as REDD.

Future studies

  • Mangrove restoration in Sumatra, Indonesia, in collaboration with the French NGO Planete Urgence and local Indonesian partners
  • Long-term surface elevation trends and vulnerability of mangroves to SLR, in collaboration with the US Geological Survey

Principal Investigators: Edward L. Webb (NUS), Tjeerd Bouma (Deltares)

Research work on mangroves is continued by Daniel Friess at the NUS Mangrove Lab.

Interesting Observations / Key Findings

  • Remote sensing has quantified mangrove deforestation over the last 3 decades; for example, mangrove area declined from 1363.34 sq km in 1990 to 1221.48 sq km in 2000, a deforestation rate of 1.04% per year. Urbanization was the main driver of mangrove loss, especially the construction of harbour facilities and power plants along the coast of Selangor to power Kuala Lumpur. Remote sensing is ongoing for mangrove cover in Myanmar, where we are showing change in mangrove extent in response to human land use change and cyclone damage.

Figure – multispectral mapping of mangrove distribution in Langkawi, west coast Peninsular Malaysia

mangrove_update

  • We installed Surface Elevation Tables into two sites in Singapore (see http://www.pwrc.usgs.gov/set/ for methodology). These instruments are drilled > 14 m through the mangrove peat layer, and are able to measure small-scale change in surface elevation change. This data is essential for comparison with sea level rise trends, in order to estimate the vulnerability of mangrove sites to climate change.

Figure – drilling of SET rods >14 m into the soil layer in Sungei Buloh mangrove, Singapore

mangrove_update

  • We have elucidated the main thresholds to seedling establishment and dislodgements through a combination of flume and field experimentation.

Figure – moment of dislodgement of an Avicennia seedling during flume experimentation

mangrove_update

Figure – dramatic mangrove loss in Singapore in the 2nd half of the 20th century

mangrove_update

Publications

Selection of Journal articles

  • Friess DA, Krauss KW, Horstman E, Balke T, Bouma TJ and Webb EL. Accepted. Are all intertidal wetlands naturally created equal? Bottlenecks, thresholds and knowledge gaps to mangrove and saltmarsh ecosystems. Biological Reviews xx
  • Friess DA and Webb EL. 2011. Bad data equals bad policy: how to trust rates of ecosystem loss when there is so much uncertainty? Environmental Conservation38: 1-5.
  • Horstman et al. 2011. Measuring short-term hydrodynamics in coastal wetlands: comparing the use of ADV, ADCP and HR-ADCP. Coastal Engineering 32

Proceedings

  • Friess DA and Webb EL. Accepted. The role of remote sensing to provide robust baselines of mangrove extent for conservation policy. Proc. of the Society of Wetland Scientists, Asian Chapter.
  • Webb EL, Friess DA and Krauss KW. Accepted. A global standard for monitoring coastal wetland vulnerability to climate change. Proc. of the Society of Wetland Scientists, Asian Chapter.
  • Bouma TJ et al. Accepted. Sediment and ecology: how to minimize impacts of dredging and create opportunities for restoration on tropical coasts? Proc. of CEDC dredging conference.
  • Friess DA and Webb EL. 2011. Uncertainty in ‘evidence-based’ policy – a strategy to improve our baselines for mangrove conservation. Proc. 5th Asian Wetland Symposium, 1-8.