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Processes affecting the spatial distribution of seagrass meadow sedimentary material on Yao Yai Island, Thailand
Quak, M.S.Y.; Ziegler, A.D.; Benner, S.G.; Evans, S.; Todd, P.A.; Gillis, L.G.; Vongtanaboon, S.; Jachowski, N.; Bouma, T.J. (2016). Processes affecting the spatial distribution of seagrass meadow sedimentary material on Yao Yai Island, Thailand. Est., Coast. and Shelf Sci. 182: 136-145. dx.doi.org/10.1016/j.ecss.2016.09.018
In: Estuarine, Coastal and Shelf Science. Academic Press: London; New York. ISSN 0272-7714; e-ISSN 1096-0015, meer
Peer reviewed article  
Beschikbaar in  Auteurs 
Author keywords
    Nutrient cycling; Island tourism and development; C and N isotopic tracers; Mangroves; Erosion and land degradation; Dredging
Auteurs  Top 
  • Quak, M.S.Y.
  • Ziegler, A.D.
  • Benner, S.G.
  • Evans, S.
  • Todd, P.A.
  • Gillis, L.G., meer
  • Vongtanaboon, S.
  • Jachowski, N.
  • Bouma, T.J., meer
Abstract
    Many islands throughout SE Asia are experiencing rapid development and land-cover conversion thatpotentially threaten sensitive coastal ecosystems, such as seagrasses, through increased loading ofsediment and nutrients originating from disturbed catchments draining to the sea. To evaluate this threatfor one such island in Southern Thailand (Yao Yai), we perform sediment source tracing via end-membermixing analysis using stable isotopes d13C and d15N in organic matter to explore sediment loading in aseagrass meadow. The analysis indicates that sedimentary material in the meadow originates mostlyfrom ocean-associated sources (~62% from seagrass detritus, seston, and ocean sediments). Terrestrialmaterial comprises ~19% of the organic material found in the seagrass meadow, with another 20%originating from an adjacent mangrove forest. Approximately one-fourth of the seagrass meadow material(24%) is detritus that has been (re)deposited internally. The high contribution of terrestrial-derivedorganic matter deposited near the river mouth demonstrates that substantial quantities of sediment arebeing transferred from upslope erosion sources into the seagrass meadow. However, only a small amountof this material is deposited throughout the entire bay because much of the terrestrial- and mangrovederivedsediment is transferred to the open ocean via channels that are periodically dredged to allowboat access to two small inland harbours. This positive affect of dredging has not received very muchattention in existing literature. River water flowing to the channels during falling tide delivers sedimentto these efficient pathways, where much of it bypasses the seagrass meadow at periods of time whensediment deposition would normally be the greatest. There is growing concern that ongoing land-coverchanges and planned urbanization related to tourism and agriculture on the island may boost sediment/nutrients above a critical threshold, beyond that revealed in our baseline survey. Our tracer-basedsediment source approach did not corroborate our observations of substantial erosion and land degradationin the upper catchmentdbut this could be a result of sediment flushing through the dredgedchannels. We encourage others to combine such methods with sediment budgeting approaches totriangulate results for consistency. Finally, from an ecological perspective, the high presence of seagrassdetritus we found in bay sediments suggests seagrass is potentially a key source of nutrients for themeadow itself, as well as other connected ecosystems.
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